Chapter 16: Reproductive System
Human Life Cycle
i. Puberty is the sequence of events where a child becomes a sexually competent young adult.
1. Sexual maturity occurs between ages 11 and 13 in girls, and 14 and 16 in boys.
2. At the completion of puberty, the individual is capable of producing children.
ii. The Reproductive Organs have the following functions:
1. Males produce sperm within testes, and females produce eggs within the ovaries.
2. Male’s nurture and transport sperm in ducts until they exit the penis, and females transport eggs in the uterine tubes to the uterus.
3. The male penis functions to deliver sperm to the female vagina, which functions to receive the sperm. The vagina also transports menstrual fluid to the exterior and is the birth canal.
4. The uterus of the female allows the fertilized egg to develop within her body. After birth, the female breast provides nourishment in the form of milk.
5. The testes and ovaries produce the sex hormones that maintain the testes and ovaries and have a profound effect on the body because they bring about masculinization and feminization of various features. In females, the sex hormones also allow a pregnancy to continue.
iii. Mitosis and Meiosis
1. Mitosis
a. Duplication division: when a cell divides, the new cells also have 46 chromosomes (the cell produces and exact copy of its self).
b. Takes place during the growth and repair of tissues
2. Meiosis
a. Reduction division: during cell division the chromosome number is reduced from the normal 46 to 23 chromosomes.
b. Happens in the testes during the production of sperm, and in the ovaries during the production of eggs.
c. When the egg is fertilized with the sperm to form a zygote there is now 46 chromosomes.
Male Reproductive System
i. Organs
1. Testes: produce sperm and sex hormones
2. Epididymides: ducts where sperm mature and some sperm are stored.
3. Vasa Deferentia: Conduct and store sperm.
4. Seminal Vesicles: Contribute nutrients and fluid to semen.
5. Prostate Gland: Contributes fluid to semen.
6. Urethra: conducts sperm.
7. Bulbourethral glands: contribute mucus-containing fluid to semen.
8. Penis: Organ of sexual intercourse.
ii. Orgasm in Males
1. The Penis has a long shaft and an enlarged tip called the glans penis.
2. Spongy erectile tissue containing distensible blood spaces extends through the shaft of the penis.
3. During sexual arousal, autonomic nerves release nitric oxide, NO.
4. This leads to the production of cGMP (cyclic guanosine monophosphate), which causes the smooth muscle of incoming arterial walls to relax and the erectile tissue to fill with blood, causing the penis to become erect.
5. During an erection, a sphincter closes off the bladder so that no urine enters the urethra.
6. As sexual stimulation intensifies, sperm enter the urethra from each vas deferens, and the glands contribute secretions to the seminal fluid.
7. Once seminal fluid is in the urethra, rhythmic muscle contraction causes it to be expelled from the penis in spurts.
8. Following ejaculation the penis returns to it’s normal flaccid state.
iii. Male Gonads, the Testes
1. Produce sperm and the male sex hormones.
2. Lie outside the abdominal cavity in the scrotum.
a. The scrotum helps regulate the temperature of the testes by holding them closer or farther away from the body.
3. The testes begin their development in the abdominal cavity but descend into the scrotum during the last 2 months of fetal development.
4. Seminiferous Tubules and Interstitial Cells
a. The testes are composed of compartments called lobules.
b. Each lobule contains 1-3 seminiferous tubules.
c. Seminiferous tubules are packed with cells undergoing spermatogenesis (the production of sperm).
d. Production of Sperm:
i. Spermatogonia divide to produce primary spermatocytes
ii. The spermatocytes undergo meiosis I to produce secondary spermatocytes, each with 23 chromosomes.
iii. Secondary spermatocytes undergo meiosis II, to produce 4 spermatids, which then differentiate into sperm.
e. Sperm have 3 distinct parts:
i. Head
1. Contains a nucleus covered by a cap called the acrosome, which stores enzymes needed to penetrate the egg.
ii. Middle
1. Mitochondria in the middle provide energy to move the tail.
iii. Tail
1. Is a flagellum
5. Interstitial Cells
a. Secrete the male sex hormones and androgens
b. Lie between the seminiferous tubules.
iv. Hormonal Regulation in Males
1. The hypothalamus has ultimate control of the testes sexual function. It secretes gonadotropin-releasing hormone (GnRH).
2. GnRH stimulates the anterior pituitary to secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
3. FSH promotes the production of sperm in the seminiferous tubules.
4. LH controls the production of testosterone by the interstitial cells.
5. When testosterone in the blood rises or falls to a certain level the hypothalamus and anterior pituitary decrease or increase their secretion of GnRH and LH.
6. Testosterone
a. Main sex hormone in males.
b. Essential for normal development and functioning of the male sex organs.
c. Maintains the male secondary sex characteristics that develop at puberty.
Female Reproductive System
i. Organs:
1. Ovaries: produce eggs and sex hormones
2. Oviducts: conduct eggs; location of fertilization.
3. Uterus: houses developing fetus.
4. Cervix: contains opening to uterus.
5. Vagina: receives penis during sexual intercourse; serves as birth canal and as an exit for menstrual flow.
ii. The Genital Tract
1. Oviducts extend from uterus to the ovaries, they are not attached, and they have fimbriae, which are finger like projections that sweep the released egg into the oviduct.
2. The egg, once in the oviduct is propelled by ciliary and tubular muscle contraction toward the uterus.
3. The life cycle of an egg is only 6-24 hours, unless fertilization occurs.
4. Fertilization causes the formation of a zygote, which usually takes place in the oviduct, after several days it will reach the uterus where implantation occurs.
5. The uterus is a thick walled, muscular organ about the shape of an inverted pear.
6. The oviducts join the uterus at the upper end.
7. The cervix is located at the lower end.
8. The lining of the uterus is the endometrium.
a. Has 2 layers
i. Basal Layer: Outer layer
ii. Inner layer: functional layer
9. The endometrium participates in the formation of the placenta, which supplies nutrients needed for embryonic and fetal development.
10. The Vagina is a tube that lies at a 45-degree angle to the small of the back.
11. The mucosal lining of the vagina lies in folds, which allows it to expand.
iii. External Genitals
1. Are collectively known as the vulva
2. Labia Majora: 2 large hair covered folds that extend backward from the mons pubis.
3. Mons Pubis: a fatty prominence underlying the pubic hair.
4. Labia Minora: 2 small folds lying just inside the labia majora, they extend foreword from the vaginal opening to encircle and form a foreskin for the glans clitoris.
5. Glans Clitoris: the organ of sexual arousal contains a shaft of erectile tissue that becomes engorged with blood during sexual stimulation.
6. Vagina: cleft between the labia minora.
iv. Orgasm in Females
1. Upon sexual stimulation, the labia minora, the vaginal wall, and the clitoris become engorged with blood.
2. The Labia majora enlarge, redden, and spread away from the vaginal opening.
3. The vagina expands and elongates.
4. Blood vessels in the vaginal wall release small droplets of fluid that seep into the vagina to lubricate it.
5. Clitoris plays a significant role in the female sexual response; it can swell to 2 or 3 times its usual size.
6. The thrusting of the penis and the pressure of the pubic symphysis of the partners act to stimulate the clitoris.
Female Hormone Levels
i. Ovarian Cycle: Nonpregnant
1. An ovary contains many follicles; each one contains an immature egg called an oocyte.
2. Only a small number of follicles ever mature because a female usually produces only 1 egg each month during the reproductive years.
3. As the follicle matures, it changes from a primary to a secondary vesicular follicle.
4. Oogenesis
a. A primary oocyte undergoes meiosis I, resulting cells are haploid with 23 chromosomes.
b. The secondary oocyte undergoes meiosis II, only if it is fertilized by a sperm cell.
c. If it remains unfertilized it never completes meiosis and dies shortly after being released from the ovary.
5. Ovulation: occurs when the vesicular follicle bursts, releasing the oocyte surrounded by a clear membrane.
6. Phases of the Ovarian Cycle
a. The hypothalamus has ultimate control of the ovaries sexual function.
b. The hypothalamus secretes GnRH, which stimulates the anterior pituitary to produce FSH and LH.
c. FSH and LH control the ovarian cycle.
d. The follicle phase: the first half, FSH promotes the development of follicles that primarily secrete estrogen.
e. As the estrogen level in the blood rises, it exerts feedback control over the anterior pituitary secretion of FSH so that the follicle phase comes to an end.
f. A positive feed back effect, an estrogen spike, causes a sudden secretion of GnRH; this leads to a surge of LH.
g. Now the luteal phase begins, LH promotes the development of the corpus luteum, which secretes progesterone.
h. When pregnancy does not occur the corpus luteum regresses and a new cycle begins with menstruation.
ii. Estrogen and Progesterone
1. Estrogen is largely responsible for the secondary sex characteristics in females.
2. Estrogen and progesterone are both required for breast development.
iii. Uterine Cycle: Nonpregnant
1. Estrogen and progesterone affect the endometrium, causing the uterus to undergo a cyclical series of events.
2. The cycle is 28 days
a. Days 1-5: low level of estrogen and progesterone cause the endometrium to disintegrate and its blood vessels to rupture. On day 1 of the cycle, a flow of blood and tissues (menses) passes out of the vagina during menstruation.
b. Days 6-13: increased production of estrogen causes the endometrium to thicken and become vascular and glandular, the proliferative phase
c. Day 14: ovulation usually occurs.
d. Days 15-28: increased production of progesterone by the corpus luteum causes the endometrium to double or triple in thickness and the uterine glands to mature, the secretory phase.
e. The endometrium is now prepared to receive the developing embryo.
f. If this does not occur the corpus luteum regresses, and the endometrium breaks down during menstruation.
iv. Fertilization and Pregnancy
1. Following unprotected sexual intercourse, many sperm will make their way into the oviduct, where the egg is located following ovulation.
2. One sperm fertilizes the egg, and it becomes a zygote, which begins development as it travels down the oviduct to the uterus.
3. The developing embryo implants in the endometrium several days following fertilization.
4. The placenta sustains the developing embryo and later the fetus.
5. The placenta originates from maternal and fetal tissues.
6. The placenta is the region of exchange of molecules between maternal and fetal blood.
7. The placenta produces human chorionic gonadotropin (HCG).
8. Rising amounts of HCG stimulates the corpus luteum to produce increasing amounts of progesterone.
9. This progesterone shuts down the hypothalamus and anterior pituitary so that no new follicles begin in the ovary.
10. Eventually the placenta produces the progesterone and some estrogen, the corpus luteum is no longer needed and it regresses.
Control of Reproduction
i. Birth Control Methods
1. Abstinence: not engaging in sexual intercourse.
2. Contraceptives: medications and devices used to reduce the chance of pregnancy
a. Birth control pills: contains a combination of estrogen and progesterone shuts down the pituitary production of FSH and LH so that no follicle in the ovary begins to develop.
b. Intrauterine Device (IUD): a small piece of molded plastic inserted into the uterus, preventing implantation of the egg.
c. Diaphragm: a soft latex cup with a rim that lodges behind the pubic bone and fits over the cervix.
d. Female Condom: a large polyurethane tube with a flexible ring that fits onto the cervix.
e. Male Condom: a latex sheath that fits over the erect penis.
f. Contraceptive implants: synthetic progesterone that prevents ovulation by disrupting the ovarian cycle, a capsule is implanted under the skin on the upper arm.
g. Contraceptive Injections: injections of progesterone only, or a combination of estrogen and progesterone.
h. Contraceptive Vaccines: a vaccine intended to immunize women against HCG.
3. Vasectomy and Tubal Ligation
a. Vasectomy: consists of cutting and sealing the vas deferens on each side so that sperm are unable to reach the seminal fluid that is ejected at the time of orgasm.
b. Tubal Ligation: consists of cutting and sealing the oviducts, preventing the passage of the egg through the oviducts.
4. Morning-After Pills
a. A medication that will prevent pregnancy after unprotected intercourse.
b. The medication can begin from one to several days after unprotected intercourse.
ii. Infertility
1. The failure of a couple to achieve pregnancy after one year of regular unprotected sex.
2. Causes of Infertility
a. Low sperm count, or large production of abnormal sperm.
b. A lifestyle coupled with smoking and drinking are most often the cause of male infertility.
c. Body weight appears to be the most significant factor causing female infertility.
d. Blocked oviducts due to pelvic inflammatory disease and endometriosis.
3. Assisted Reproductive Technologies
a. Artificial Insemination by Donor (AID): sperm are placed in the vagina by a physician
b. In Vitro Fertilization (IVF): conception occurs in laboratory glassware, after 2-4 days the embryos are transferred to the uterus.
c. Gamete Intrafallopian Transfer (GIFT): the same as in vitro fertilization, except the eggs and sperm are placed in the oviducts immediately after they have been brought together.
d. Surrogate Mothers: women are contracted and paid to have babies; the sperm and the egg can be contributed from the contracting parents.
e. Intracytoplasmic Sperm Injection (ICSI): a single sperm is injected into an egg.
Sexually Transmitted Diseases
i. STD’s caused by viruses: are not curable.
1. HIV infection
2. Genital warts
3. Genital herpes
4. Hepatitis
ii. STD’s caused by Bacteria: are curable with antibiotics.
1. Chlamydeous
2. Gonorrhea
3. Syphilis
Chapter 17: Development and Aging
Fertilization: the union of a sperm and egg to form a zygote.
i. Steps of fertilization
1. The sperm uses its tail (flagellum) to swim towards the egg.
2. The nucleus from the sperm head fuses with the egg nucleus.
3. An extra cellular matrix called the zona pellucida surrounds the plasma membrane of the egg.
4. A few layers of adhering follicular cells called the corona radiata surround the zona pellucida.
5. During fertilization several sperm penetrate the corona radiata, and attempt to penetrate the zona pellucida, but only one sperm enters the egg.
6. When a sperm binds to the egg their plasma membranes fuse, and the sperm enters the egg.
7. Fusion of the sperm nucleus and egg nucleus follows.
8. As soon as a sperm touches an egg the egg’s plasma membrane depolarizes, preventing the binding of any other sperm.
9. Vesicles called cortical granules release enzymes that cause the zona pellucida to become impenetrable.
Pre-Embryonic and Embryonic Development
i. Processes of Development: as a human develops, these processes occur
1. Cleavage:
a. Immediately after fertilization the zygote begins to divide.
b. There is not an increase in size during these divisions.
c. Cell division is mitotic; each cell receives a full complement of chromosomes and genes.
2. Growth:
a. During embryonic development, cell division is accompanied by an increase in the size of the daughter cells.
3. Morphogenesis:
a. Refers to the shaping of the embryo.
b. By movements of certain cells, the embryo begins to assume various shapes.
4. Differentiation:
a. When cells take on a specific structure.
ii. Extraembryonic Membranes
1. Are located outside of the embryo
2. Chorion: develops into the first half of the placenta.
3. Allantois: extends away from the embryo like the yolk sac. It accumulates small amounts of urine produced by the fetal kidneys. Its blood vessels become the umbilical cord.
4. Yolk Sac: Is the first embryonic membrane to appear, it is the first site of blood cell production.
5. Amnion: it enlarges as the embryo and then fetus enlarges. It contains fluid to cushion and protect the embryo.
iii. Stages of Development
1. Pre-Embryonic Development
a. Occurs during the first week.
b. After fertilization the zygote divides repeatedly as it passes down the oviducts to the uterus.
c. Morula: a compact ball of embryonic cells that becomes a blastocyst.
d. The cells of the blastocyst arrange themselves so that there is an inner cell mass surrounded by an outer layer of cells.
e. The inner cell mass becomes the embryo; the layer of cells becomes the Chorion.
2. Embryonic Development
a. Starts with the second week and lasts until the end of the second month of development.
b. Second Week
i. At the end of the first week the embryo begins the process of implanting itself in the wall of the uterus.
ii. During implantation, the Chorion secretes enzymes to digest away some tissue and blood vessels of the endometrium of the uterus.
iii. The Chorion also begins to secrete HCG.
iv. HCG is the basis for the pregnancy test.
v. HCG serves to maintain the corpus luteum past the time it normally disintegrates.
vi. The corpus luteum secretes progesterone, the endometrium is maintained, and menstruation does not occur.
vii. The embryo is about the size of a period at the end of a sentence.
viii. As the week progresses the inner cell mass becomes the embryonic disk, and 2 more Extraembryonic membranes form.
ix. Gastrulation turns the inner cell mass into the embryonic disk.
x. By the time gastrulation is complete, the embryonic disk has become an embryo with three primary germ layers:
1. Ectoderm
2. Mesoderm
3. Endoderm
xi. All of the organs of an individual can be traced back to one of the primary germ layers.
c. Third Week
i. The nervous system is the first organ system to be visually evident.
ii. Development of the heart begins in the third week and continues into the fourth week.
d. Fourth and Fifth Weeks
i. At four weeks the embryo is barely bigger than the height of this print.
ii. During the fourth week the umbilical cord is fully formed
iii. Limb buds appear, which later develop into the arms and legs.
iv. During the fifth week the head enlarges, and the sense organs become more prominent.
e. Sixth through Eighth Weeks
i. The embryo changes to a form that is easily recognized as a human being.
ii. The nervous system is developed well enough to permit reflex actions.
iii. At the end of this period the embryo is about 38mm long.
iv. All organ systems have been established.
Fetal Development
i. Events of fetal Development
1. Third month
a. Gender can be distinguished, fingernail appear.
2. Fourth Month
a. Skeleton is visible and hair begins to appear.
b. The fetus is about 150mm long, and weighs about170 grams.
3. Fifth Month
a. Protective coating and vernix caseosa, begins to be deposited, the heartbeat can be heard.
4. Sixth Month
a. Body is covered with lanugo, skin is wrinkled and reddish.
5. Seventh Month
a. Testes descend into the scrotum, eyes are open.
b. The fetus is about 12 in long and weighs 3 lb.
6. Eighth Month
a. Body hair begins to disappear; subcutaneous fat begins to be deposited.
7. Ninth Month
a. Fetus is ready for birth; it is about 20 ½ in long and weighs about 7 ½ lb.
ii. Path of Fetal Blood
1. The umbilical cord stretches between the placenta and the fetus.
2. The umbilical cord is the lifeline of the fetus because it contains the umbilical arteries and veins.
3. Blood within the fetal aorta travels to its various branches, including the iliac arteries.
4. The iliac arteries connect to the umbilical arteries carrying oxygen poor blood to the placenta.
5. The umbilical vein carries blood rich in nutrients and oxygen from the placenta to the fetus.
6. The umbilical vein enters the liver and then joins the venous duct.
7. The venous duct merges with the inferior vena cava, which returns blood to the right atrium.
8. The mixed blood enters the heart and is shunted to the left atrium through the oval opening.
9. The left ventricle pumps blood into the aorta.
10. Oxygen poor blood that enters the right atrium is pumped into the pulmonary trunk, but joins the aorta by way of arterial duct.
iii. Development of Male and Female Genitals
1. Normal Development of the Genitals
a. Internal Genitals
i. Gonads start developing during the seventh week of development.
ii. The tissue that gives rise to the gonads is indifferent because it can become testes or ovaries depending on the action of hormones.
iii. At six weeks both males and females have the same types of ducts.
iv. If a gene called SRY is present, testes develop and testosterone produced stimulates the wolffian ducts to become male genital ducts.
v. In the absence of the SRY gene, ovaries develop instead of testes from the same indifferent tissue.
b. External Genitals
i. At six weeks a small bud appears between the legs, this can develop into the male penis or female clitoris.
ii. At nine weeks a urogenital groove bordered by two swellings appears.
iii. At 14 weeks this groove disappears in males, and in females it persists and becomes the vaginal opening.
Pregnancy and Birth
i. Pregnancy
1. Energy Level Fluctuates
a. When first pregnant, the mother may experience nausea and vomiting, loss of appetite, and fatigue.
b. The Uterus Relaxes
i. Progesterone decreases uterine uterine motility by relaxing smooth muscle.
ii. Blood volume increases from 5L to 7L and peaks during 28-32 weeks of pregnancy.
ii. Birth
1. The uterus has contractions throughout pregnancy. At first they are light, lasting about 20-30 seconds and occurring every 15-20 min.
2. Near the end of pregnancy the contractions become stronger and more frequent, they are called braxton hicks contractions.
3. True labor is marked by uterine contractions that occur regularly every 15-20 min and last 40 seconds or longer.
4. Uterine contractions are induced by a stretching of the cervix, which also brings about the release of oxytocin.
5. Oxytocin stimulates the uterine muscles.
6. Uterine contractions push the fetus downward, and the cervix stretches even more.
7. Stage 1
a. Uterine contractions of labor occur in such a way that the cervical canal slowly disappears as the lower part of the uterus is pulled upward toward the baby’s head. This process is called effacement.
b. During this stage the amniotic membrane usually ruptures.
8. Stage 2
a. Contractions occur every 1-2 minutes and last about 1 minute.
b. These contractions are accompanied by a desire to push or bear down.
c. As soon as the head is delivered, the physician may hold the head and guide it downward, while one shoulder and then the other emerges. The rest of the baby follows easily.
9. Stage 3
a. The placenta is delivered during the third stage.
b. After delivery uterine muscular contractions shrink the uterus and dislodge the placenta.
c. The placenta is expelled into the vagina, it is then delivered.
Development After Birth
i. Hypothesis of Aging:
1. Genetic in Origin
a. Some research indicates that aging has a genetic basis.
b. Mitochondrial hypothesis of aging
i. Defective mitochondria produce more free radicals than usual.
ii. Free radicals are unstable molecules that carry an extra electron.
iii. Eventually these molecules are unable to function and the cell is destroyed.
2. Whole-Body Process
a. A decline in the hormonal system affects many different organs of the body.
b. The immune system no longer performs as it once did.
3. Extrinsic Factors
a. Much of what is attributed to aging is due to years of poor health habits.
ii. Effect of Age on Body Systems
1. Skin
a. Skin becomes thinner and less elastic because the number of elastic fibers decreases and the collagen fibers undergo cross-linking.
b. There is less adipose tissue in the subcutaneous layer.
2. Processing and Transporting
a. The heart shrinks
b. Arteries become more rigid
c. Blood flow to the liver is reduced, and does not metabolize drugs as efficiently as before.
d. Growing inelasticity of lung tissue reduces ventilation.
e. Blood supply to the kidneys is reduced; they become smaller and less efficient at filtering wastes.
3. Integration and Coordination
a. Reaction time slows; more stimulation is needed for hearing, taste, and smell receptors to function as before.
b. Loss of skeletal muscle mass occurs.
c. A decline in bone density also occurs.
4. The Reproductive System
a. Females undergo menopause
b. Males undergo andropause.
Chapter 22: Human Evolution
Origin of Life
i. The Primitive Earth
1. the sun and planets probably formed over a 10-billion-year period from aggregates of dust particles and debris.
2. the first atmosphere was most likely formed by gases escaping from volcanoes
3. It would have consisted mostly of water vapor, nitrogen, and carbon dioxide, with only small amounts of hydrogen and carbon monoxide.
4. there was little if any free oxygen.
5. the atmosphere was extremely hot.
6. water existed only as a gas and formed dense thick clouds.
7. as the earth cooled water vapor condensed to liquid water, and rain began to fall.
8. It rained over hundreds of millions of years producing the oceans.
ii. Small Organic Molecules
1. primitive gases may have reacted with one another to produce small organic compounds, such as nucleotides and amino acids.
iii. Macromolecules
1. The newly formed small organic molecules joined to produce organic macromolecules.
2. There are two hypothesis of special interest concerning this stage in the origin of life.
a. RNA-first hypothesis
i. Suggests that only the molecule RNA was needed at this time to progress toward formation of the first cells.
b. Protein-first hypothesis
i. It was suggested that amino acids collected in shallow puddles along the rocky shore, and the heat of the sun caused them to form proteinoids.
1. Protenoids: small polypeptides that have some catalytic properties.
ii. When proteinoids returned to water, they form microspheres, structures composed only of protein that have many of the properties of a cell.
iv. The Protocell
1. When lipids are made available to microspheres, the two tend to become associated, producing a lipid-protein membrane.
2. Are able to carry on metabolism but not reproduce.
3. Used the small organic molecules in the ocean as food.
4. Was most likely a heterotroph: an organism that takes in preformed food.
5. Would have been a fermenter because there was no free oxygen.
v. The True Cell
1. Can reproduce, and in today’s cells, DNA replicates before cell division occurs.
2. How did the first cell acquire DNA and enzymatic proteins?
a. RNA-first hypothesis
i. First cell had RNA genes that could have specified protein synthesis.
ii. Some of the proteins formed would have been enzymes.
iii. Perhaps one of these enzymes used RNA as a template to form DNA.
b. Protein-first hypothesis
i. Some of the proteins in the Protocell would have evolved the enzymatic ability to synthesize DNA from nucleotides in the ocean.
ii. Then DNA would have gone on to specify protein synthesis, and in this way the cell would have acquired all its enzymes, including the ones to replicate DNA.
Biological Evolution
i. Common Descent
1. The types of evidence that convinced Darwin that common descent occurs were fossil, anatomical, and biographical.
a. Fossil Evidence Supports Evolution
i. Are the best evidence for evolution because they are the actual remains of species that lived on earth at least 10,000 years ago and up to billions of years ago.
ii. Can be traces of past life or any other direct evidence that past life existed
iii. Traces include trails, footprints, burrows, worm casts, preserved droppings.
iv. Can also be pieces of bones, impressions of plants pressed into shale, insects trapped into tree resin.
v. Most fossils are found embedded in or recently eroded from sedimentary rock.
b. Biographical Evidence Supports Evolution
i. Biography is the study of the distribution of plants and animals in different places throughout the world.
ii. Such distributions are consistent with the hypothesis that life-forms evolved in a particular locale and then they may spread out.
c. Anatomical Evidence Supports Evolution
i. Darwin was able to show that a common descent hypothesis offers a plausible explanation for anatomical similarities among organisms.
ii. Vertebrae forelimbs are used for:
1. Flight (birds and bats)
2. Orientation during swimming (whales and seals)
3. Running (horses)
4. Climbing (arboreal lizards)
5. Swinging from tree branches (monkeys)
iii. All vertebrae forelimbs contain the same sets of bones organized in similar ways.
iv. The basic forelimb plan belonged to a common ancestor, and then the plan was modified in the succeeding groups as each continued its own evolutionary pathway.
d. Biochemical Evidence Supports Evolution
i. Almost all living organisms use the same basic biochemical molecules, including DNA, ATP, and many identical or nearly identical enzymes.
ii. Intelligent Design
1. The diversity of life could have never arisen without the involvement of an intelligent agent.
2. Many scientists and religions, argue that it is faith based and not science because it is not possible to test in a scientific way.
iii. Natural Selection
1. During adaptation, a species becomes suited to its environment.
2. The critical elements for natural selection process are variation, competition for limited resources such as food, and adaptation as an end result.
a. Variation: individual members of a species vary in physical characteristics. Physical variations can be passed from generation to generation.
b. Competition for limited resources: The number in each generation usually stays the same, because resources are limited and competition for resources results in unequal reproduction among members of a population.
c. Adaptation: The members of a population with advantageous traits capture more resources and are more likely to reproduce and pass on these traits. Overtime the environment selects for the better-adapted traits.
Classification of Humans
i. DNA Data and Human Evolution
1. Researchers are depending more and more on DNA data to trace the history of life.
2. Major decisions regarding the history of life are now being made on the basis of DNA/rRNA/protein sequencing data.
ii. Humans Are Primates
1. Primates are adapted to an arboreal life: for living in trees.
2. Primates have 2 suborders:
a. Prosimians: lemurs, tarsiers, and lorises.
b. Anthropoids: monkeys, apes, humans.
3. Mobile Forelimbs and Hind Limbs
a. Primate limbs are mobile, the hands and feet both have 5 digits each.
b. Many primates have both an opposable big toe and thumb; this results in a grip that is powerful and precise.
c. Humans only have an opposable thumb.
4. Binocular Vision
a. In primates the snout is shortened, allowing the eyes to move to the front of the head. Stereoscopic vision (depth perception) that results permit primates to make accurate judgments about the distance and position of adjoining trees and limbs.
b. Humans and apes have three different cone cells, which are able to discriminate between greens, blues, and reds.
5. Large, Complex Brain
a. The brain size is smallest in prosimians and largest in modern humans.
b. The cerebral cortex expands so much that it becomes extensively folded in humans.
c. The portion devoted to smell gets smaller, and the portions devoted to sight increase in size and complexity during primate evolution.
6. Reduced Reproductive Rate
a. One birth at a time is the norm for primates; it is difficult to care for several offspring while moving from limb to limb.
b. The juvenile period of dependency is extended, and there is an emphasis on learned behavior and complex social interactions.
iii. Comparing Human Skeleton to the Chimpanzee Skeleton
1. The genomes of humans and chimpanzees are 99% identical.
2. Humans but not chimps are adapted for an upright stance:
a. In humans the spine exits inferior to the center of the skull, this places the skull in the midline of the body.
b. The longer S-shaped spine of humans places the trunk’s center of gravity squarely over the feet.
c. The broader pelvis and hip joint of humans keeps them from swaying when they walk.
d. The longer neck of the femur in humans causes the femur to angle inward at the knees
e. The human knee is modified to support the body’s weight.
f. The human toe is not opposable, instead the foot has an arch, which allows humans to walk long distances and run with less chance of injury.
Evolution of Hominids
i. The First Hominids
1. Hominid is a term that refers to our branch of the evolutionary tree.
2. Any fossil placed in the hominid line of descent is closer to us than to one of the African Apes.
3. When any 2 lines of descent, called a lineage, first diverge from a common ancestor, the genes and proteins of the 2 lineages are nearly identical.
4. Many genetic changes, which lead to RNA and protein changes. Many genetic changes are neutral and accumulate at a fairly constant rate; such changes are used as a molecular clock to indicate the relatedness of 2 groups and when they diverged from each other.
5. Hominids split from the ape line of descent about 7 MYA.
ii. Hominid Features
1. Bipedal Posture (walking on 2 feet)
a. The first hominid began to assume a bipedal posture while it lived in the trees.
b. The first hominids environment is thought to have included some forest, woodland, and grassland.
c. While still living in trees, they may have upright on large branches to collect fruit from overhead.
d. When foraging on the ground among bushes, it would have been easier to move around on their hind limbs.
2. The shape of the face
a. Humans have a flatter face and a more pronounced chin than do the apes because the human jaw is shorter than the apes.
3. Brain Size
a. Chimpanzees have a brain size of about 400 cm cubed, and humans have a brain size of about 1300 cm cubed.
iii. Earliest Fossil Hominids
1. Sahelanthropus Tchadensis
a. Oldest of fossils found, dated 7MYA.
b. Found in Chad, in central Africa.
c. The only find was a skull, the canines are smaller and the tooth enamel is thicker than that of an apes.
d. The braincase is very apelike, and it is impossible to tell if this hominid walked upright.
2. Orrorin Tugenensis
a. Dated 6 MYA
b. Found in eastern Africa
c. The limb anatomy suggests a bipedal posture
d. The canine teeth are large and pointed.
e. The arm and finger bones retain adaptations for climbing.
3. Ardipithecus Kadabba
a. Dated between 5.8 and 5.2 MYA
b. Found in eastern Africa
c. Is closely related to the aridipithecus Ramidus. This ardipithecine is thought to be closely related to the australopithecines.
iv. Evolution of Australopithecines
1. A group of species that evolved and diversified in Africa.
2. Some were slight of frame and called gracile.
3. Some were robust and tended to have powerful upper bodies and especially massive jaws.
4. The gracile types most likely fed on soft fruits and leaves, while the robust types had a more fibrous diet that may have included hard nuts.
5. The skull structure was suited to their particular diets.
v. Southern Africa
1. The first australopithecine to be discovered was in southern Africa, called australopithecine africanus.
2. Was a gracile type, dated about 2.8 MYA
3. A. robustus, dated from 2 to 1.5 MYA, is a robust type from southern Africa.
4. Both A. africanus and A. robustus had a brain size of about 500 cm cubed.
5. Their skull differences are due to dental and facial adaptations to different diets.
6. Limb anatomy suggests that they walked upright, but the proportions of the limbs are ape like.
vi. Eastern Africa
1. A. afarensis dated 3.18 MYA, a now famous female skeleton called Lucy.
2. The proportions of the limbs indicate that Lucy stood upright and walked bipedally.
3. The australopithecines were ape like above the waste and human like below the waste, shows that human characteristics did not evolve all at one time.
Evolution of Humans
i. Early Homo
1. Homo Habilis dated between 2.0 and 1.9 MYA, may be ancestral to modern humans.
a. Some of these fossils have a brain size as large as 775 cm cubed, which is about 45% larger than that of A. afarensis.
b. The cheek teeth are smaller than even those of the gracile australopithecines; it is likely that these early members of the genus Homo were omnivores who ate meat in addition to plants.
c. Bones near their campsites bear cut marks, indication that they used tools to strip them of meat.
d. The stone tools made by H. Habilis (handy man) are rather crude.
e. Early Homo skulls suggest that the portions of the brain associated with speech were enlarged. We can speculate that the ability to speak may have led to hunting cooperatively.
f. Both hunters and gatherers most likely ate together and shared their food, in this way society and culture could have begun.
g. Culture depends upon the capacity to speak and transmit knowledge.
2. Homo erectus
a. Are found in Africa, Asia, and Europe and dated between 1.9 and 0.3 MYA.
b. All fossils assigned the name H. erectus are similar in appearance, but enough discrepancies exist to suggest that several different species have been included in this group.
c. The Asian form is H. erectus; the African form is H. ergaster.
d. H. erectus had a larger brain (1000 cm cubed) and a flatter face than H. Habilis.
e. The nose projected, which is adaptive for a hot, dry climate because it permits water to be removed before air leaves the body.
f. H. ergaster was much taller than the hominids discussed so far, males were about 6 feet and females were about 5 feet.
g. These hominids were erect and most likely had a striding gait like ours.
h. The size of the birth canal indicates that infants were born in a immature state that required an extended period of care.
i. H. ergaster may have first appeared in Africa and than migrated into Asia and Europe.
j. Migration occurred between 1.9 and 1.6 MYA.
k. H. erectus was the first hominid to use fire and also fashioned more advanced tools than early Homos.
l. It could be that H. ergaster was a systematic hunter and brought kills to the same site over and over again, these sites could have been “home bases,” where social interaction occurred and a prolonged childhood allowed time for learning. Perhaps a language evolved and a culture more like our own developed.
ii. Evolution of Modern Humans
1. Homo sapiens (modern humans) evolved from H. erectus
2. Two hypothesis on how homo sapiens evolved
a. Multi-regional continuity Hypothesis
i. Evolution to modern humans was essentially similar in several different places.
b. Out-of-Africa hypothesis
i. H. sapiens evolved from H. erectus only in Africa, and thereafter H. sapiens migrated to Europe and Asia about 100,000 years BP.
iii. Neandertals
1. H. neandertalensis take their name from Germanys Neander Valley.
2. They had massive brow ridges, and their nose, jaws, and teeth protruded far forward.
3. The forehead was low and sloping, and the lower jaw lacked a chin.
4. Neandertals were eventually supplanted by modern humans.
5. Their brain was slightly larger than H. sapiens (1400 cm cubed compared with 1360 cm cubed).
6. Bones of the limbs were shorter and thicker than modern humans.
7. They lived in Europe and Asia during the last Ice age; their sturdy build could have helped conserve heat.
8. Most lived in caves and they manufactured a variety of stone tools.
9. They buried their dead with flowers and tools and may have had a religion.
iv. Cro-Magnons
1. The oldest fossils to be designated H. sapiens.
2. Are named after a fossil location in France
3. They had a thoroughly modern appearance.
4. Neandertal and Cro-Magnon DNA are so different that is shows that these 2 groups did not interbreed.
5. Cro-Magnons replaced the Neandertals in the Middle East and then spread to Europe where they lived side by side with the Neandertals.
6. They made advance tools
7. They hunted cooperatively, and it is suggested that they are responsible for the extinction of larger mammals like the giant sloth or the mammoth.
8. They may have been the first to have a language.
9. Their culture included art, including paintings and small sculptures made out of reindeer bones.
v. Human Variation
1. It has been hypothesized that human variations evolved because as adaptations to local environmental conditions.
a. Darker skin color is protective against the high UV intensity of bright sunlight.
b. White skin ensures vitamin D production in the skin when UV intensity is low.
2. Body shape
a. Bergman’s Rule: Animals in colder regions have a bulkier body build
b. Allen’s Rule: animals in colder regions have shorter limbs, digits, and ears.
c. Both of these effects regulate body temperature.
Chapter 23: Global Ecology and Human Interferences
The Nature of Ecosystems
i. Ecosystems
1. There are several major types of terrestrial ecosystems, called biomes.
a. Tropical Rain Forest: occurs at the equator, and is dominated by large evergreen, broad-leaved trees.
b. Savanna: is tropical grassland that supports many types of grazing animals.
c. Temperate Grasslands: receive less water than temperate forests but more water than deserts.
d. Temperate Forests: trees lose their leaves during the winter.
e. Deserts: Lack trees.
f. The Taiga: a very cold northern coniferous forest.
g. Tundra: borders the North Pole, very cold, with long winters and a short growing season.
2. Each biome contains communities of organisms adapted to the regional climate.
3. Aquatic Ecosystems are divided into those composed of fresh water and those composed of salt water.
a. The Ocean is a major marine ecosystem that covers 70% of the earth’s surface.
i. The richest marine ecosystems lie near the coasts.
ii. Coral Reefs occur offshore and marshes occur where rivers meet the sea.
b. 2 types of freshwater ecosystems
i. Standing Water: lakes, and ponds.
ii. Running Water: rivers and streams.
ii. Biotic Components of an Ecosystem
1. Abiotic components of an ecosystem are the nonliving components.
2. Biotic components of an ecosystem are the living things that can be categorized according to their food source.
a. Some populations are autotrophs, and some are heterotrophs.
3. Autotrophs
a. Require only inorganic nutrients and an outside energy source to produce organic nutrients for their own use and for all the other members of a community.
b. They are called producers, because they produce food.
c. Photosynthetic organisms produce most of the organic nutrients for the biosphere.
d. Algae carry on photosynthesis in freshwater and marine habitats.
e. Green plants are the dominant photosynthesizers on land.
4. Heterotrophs
a. Need a source of organic nutrients.
b. They are consumers, they consume food.
c. Herbivores are animals that graze directly on plants or algae.
d. Carnivores feed on other animals.
e. Three groups of consumers
i. Primary Consumers: insects
ii. Secondary Consumers: insect-eating birds
iii. Tertiary Consumers: Hawks also called top predators.
f. Detritus feeders:
i. are organisms that feed on detritus, which is decomposing particles of organic matter.
ii. They acquire nutrients by breaking down dead organic matter, including animal wastes.
iii. Decomposers perform a valuable service, they release inorganic substances that are taken up by plants once more.
5. Niche
a. A niche is the role of an organism in an ecosystem: how it gets its food and what eats it, and how it interacts with other populations in the same community.
iii. Energy Flow and Chemical Cycling
1. Every ecosystem is characterized by two phenomena:
a. Energy Flow
i. Begins when producers absorb solar energy
ii. Occurs because as nutrients pass from one population to another, all the energy content is eventually converted into heat, which dissipates in the environment
b. Chemical Cycling
i. Begins when producers take in inorganic nutrients from the physical environment.
ii. Chemicals cycle when inorganic nutrients are returned to the producers from the atmosphere or soil.
Energy Flow
i. Trophic Levels
1. is composed of all the organisms that feed at a particular link in the food chain.
2. In the grazing food web
a. Trees are producers:1st Trophic Level
b. The first series of animals are primary consumers: 2nd Trophic Level
c. The next group of animals is secondary consumers: 3rd Tropic Level.
ii. Ecological Pyramids
1. The shortness of food chains can be attributed to the loss of energy between trophic levels.
a. Only about 10% of the energy of one trophic level is available to the next trophic level.
2. The flow of energy with large losses between successive trophic levels is sometimes depicted as an ecological pyramid.
3. Energy losses between trophic levels also result in pyramids based on the number of organisms in each trophic level.
a. When constructing a pyramid base don number of organisms, problems arise.
b. Ex: each tree would contain numerous caterpillars; therefore there would be more herbivores than autotrophs.
4. Pyramids of biomass eliminate size as a factor because biomass is the number of organisms multiplied by the weight of organic matter within one organism.
Global Biogeochemical Cycles
i. The Water Cycle
1. Water Cycle
a. During evaporation , the sun’s rays cause freshwater to evaporate from seawater, and the salts are left behind. During condensation a gas is changed into a liquid.
b. Vaporized freshwater rises into the atmosphere, condenses, and then falls as precipitation; (rain, snow, hail, sleet, and fog) over the oceans and the land.
c. Water also evaporates from land and from plants (evaporation from plants is called transpiration).
d. Because land lies above sea level, gravity eventually returns all freshwater to the sea.
e. Runoff is water that flows directly into nearby streams, lakes, wetlands, or the ocean.
i. Instead of running off, some precipitation sinks, or percolates, into the ground and saturates the earth to a certain level.
ii. The top of the saturation zone is called the ground-water table, or simply, the water table.
f. Groundwater is also located in aquifers, rock layers that contain water and release it in appreciable quantities to wells or springs.
2. Human Activities
a. Humans interfere with the water cycle in 3 ways:
i. They withdraw water from the aquifers
ii. They clear vegetation from the land and build roads and buildings that prevent percolation and increase runoff
iii. They interfere with the natural processes that purify water, and instead add pollutants like sewage and chemicals to water.
ii. The Carbon Cycle
1. Carbon dioxide in the atmosphere is the exchange pool for the carbon cycle.
a. On land, plants take up carbon dioxide from the air, and through photosynthesis, they incorporate carbon into nutrients that are used by autotrophs and heterotrophs alike.
b. When organisms, including plants, respire, carbon is returned to the atmosphere as carbon dioxide.
i. Carbon dioxide recycles to plants by way of the atmosphere
ii. In aquatic ecosystems, the exchange of carbon dioxide with the atmosphere is indirect.
c. Carbon dioxide from the air combines with water to produce bicarbonate ion, a source of carbon for algae that produce food for themselves and for heterotrophs
i. When aquatic organisms respire, the carbon dioxide they give off becomes bicarbonate ion.
d. The amount of bicarbonate in the water is in equilibrium with the amount of carbon dioxide in the air.
e. Living and dead organisms contain organic carbon and serve as one of the reservoirs for the carbon cycle.
f. In the history of the earth plant and animal remains were transformed into coal, oil, and natural gas, called fossil fuels. These are also reservoirs that hold carbon.
2. Human Activities
a. The transfer rates of carbon dioxide due to photosynthesis and cellular respiration are just about even.
b. However, more carbon dioxide is being deposited in the atmosphere than is being removed.
c. This increase is due largely to the burning of fossil fuels and the destruction of forests to make way for farmland and pasture.
d. CO2 and Global Warming
i. Carbon dioxide and also other gases are being emitted due to human activities.
ii. These gases are known as greenhouse gases because they allow solar radiation to pass through but hinder the escape of infrared rays (heat) back into space.
iii. The Nitrogen Cycle
1. Nitrogen gas makes up about 78% of the atmosphere, but plants cannot make use of nitrogen gas.
2. Ammonium Formation and Use
a. Nitrogen fixation occurs when nitrogen gas is converted to ammonium, a form plants can use.
b. Some cyanobacteria in aquatic ecosystems and some free-living bacteria in soil are able to fix atmospheric nitrogen in this way.
3. Nitrate Formation and Use
a. Plants can also use nitrates as a source of nitrogen.
b. The production of nitrates is called nitrification.
c. Nitrification can occur in these ways:
i. Nitrogen gas is converted to nitrate in the atmosphere when cosmic radiation, meteor trails, and lightning provide the high energy needed for nitrogen to react with oxygen.
ii. Ammonium in the soil from various sources, including decomposition of organisms and animal wastes, is converted to nitrate by soil bacteria:
1. nitrite-producing bacteria convert ammonium to nitrite, and then nitrate-producing bacteria convert nitrite to nitrate.
iii. During assimilation, plants take up ammonia and nitrate from the soil and use these ions to produce proteins and nucleic acids.
4. Formation of Nitrogen Gas from Nitrate
a. Dentrification is the conversion of nitrate back to nitrogen gas, which enters the atmosphere.
b. Dentrifying bacteria living in the anaerobic mud of lakes, bogs, and estuaries carry out this process as a part of their own metabolism.
c. In the nitrogen cycle, Dentrification would counter balance nitrogen fixation except for human activities.
5. Human Activities
a. Human activities significantly alter the transfer rates in the nitrogen cycle by producing fertilizers from N2, they nearly double the fixation rate.
b. Fertilizer runs off into lakes and rivers and results in an overgrowth of algae and rooted aquatic plants.
c. Acid deposition occurs because nitrogen oxides and sulfur dioxide enter the atmosphere from the burning of fossil fuels.
i. Both of these gases combine with water vapor to form acids that eventually return to the earth
d. Nitrogen oxides and hydrocarbons from the burning of fossil fuels react with one another in the presence of sunlight to produce smog, which contains dangerous pollutants.
i. However during a thermal inversion, pollutants are trapped near the Earth beneath a layer of warm, stagnant air.
ii. Because the air does not circulate, pollutants can build up to dangerous levels.
iv. The Phosphorus Cycle
1. Phosphorus Cycle
a. Phosphorus trapped in oceanic sediments moves onto land after a geological upheaval.
b. On land, the very slow weathering of rocks places phosphate ions in the soil.
c. Some of this becomes available to plants, which use phosphates in a variety of molecules including phospholipids, ATP, and the nucleotides that become part of DNA and RNA.
d. Animals eat producers and incorporate some of the phosphate into teeth, bones, and shells.
e. Death and decay of all organisms and also decomposition of animal wastes do, however, make phosphate ions available to producers once again.
f. Some phosphate naturally runs off into the aquatic ecosystems, where algae acquire phosphate from the water before it becomes trapped in sediments.
g. Phosphate in marine sediments does not become available to producers on land again until a geological upheaval exposes sedimentary rocks on land.
2. Phosphorus and Water Pollution
a. Humans boost the supply of phosphate by mining phosphate ores for fertilizer and detergent productions.
i. Runoff of phosphate and nitrogen due to fertilizer use, animal wastes from livestock feedlots, and discharge from sewage treatment plants result in cultural eutrophication (overenrichment) of waterways.
Chapter 24: Human Population, Planetary Resources, and Conservation
Human Population Growth
i. The MDC’s Versus the LDC’s
1. The countries of the world can be divided into 2 groups:
a. MDC’s: The more developed countries, countries in North America and Europe with a population growth that is modest and the people enjoy a good standard of living.
i. Did not always have low population increases, between 1850 and 1950, they doubled their populations, mainly because of a decline in the death rate.
ii. The growth rate for the MDC’s as a whole is now about 0.1%, but several are not growing at all or are decreasing in size.
iii. The MDC’s are expected to increase by 52 million between 2002 and 2050, but this amount will still keep their total population at just about 1.2 billion.
b. LDC’s: The less developed countries, some countries in Asia, Africa and Latin America with a population growth that is dramatic and the majority of the population live in poverty.
i. The death rate began to decline steeply in the LDC’s following World War II with the introduction of modern medicine, but the birth rate remained high.
ii. The Growth rate peaked at about 2.5% between 1960 and 1965. Since that time, the collective growth rate for the LDC’s has declined to 1.6%, but some 46 countries have not participated in this decline. 35 of these countries are in the Sub-Saharan Africa where women on the average are having more than 5 children each.
iii. Between 2002 and 2050 the population of the LDC’s may jump from 5 billion to at least 8 billion. Some of this increase will occur in Africa, but most will occur in Asia because many deaths from AIDS are slowing the growth of the African population.
iv. Asia already has 56% of the world’s population living on 31% of its farmable land. 12 of the world’s 15 most polluted cities are in Asia.
c. Comparing Age Structure
i. The LDC’s are experiencing a population momentum because they have more women entering their reproductive years than older women leaving them.
ii. Populations have 3 age groups:
1. Prereproductive: ages 0-19
2. Reproductive: ages 20-44
3. Postreproductive: ages 45-80
iii. Replacement Reproduction is when there are more young women entering reproductive years than older women leaving them causing the population to increase. Replacement reproduction will cause most LDC’s today to have a positive growth rate.
iv. Most MDC’s, not including the US, have a stabilized age-structure diagram. Therefore, their populations are expected to remain about the same or decline if couples are having fewer than 2 children.
Human Use of Resources and Pollution
i. Land
1. Beaches and Human Habitation
a. At least 40% of the world population lives within 60 miles of a coastline, this number is expected to increase.
b. In the US over half of the population lives within 50 miles of the coastline.
c. Living right on the beach leads to beach erosion and loss of habitat for marine organisms and a loss of a buffer zone for storms.
d. An estimated 70% of the world’s beaches are eroding.
e. One reason to protect coastal wetlands is that they are spawning areas for fish and other forms of marine life. Wetlands also protect coastal areas from storms.
2. Semiarid Lands and Human Habitation
a. 40% of the Earth’s lands are already desert, and land adjacent to a desert is in danger of becoming unable to support human life if it is improperly managed by humans.
b. Desertification is the conversion of semiarid land to desert like conditions.
i. It begins when humans allow animals to overgraze the land. The soil can no longer hold rainwater, and it runs off instead of keeping the remaining plants alive or replenishing wells.
ii. Humans then remove whatever vegetation they can find; the end result is a lifeless desert, which is then abandoned.
iii. 3 quarters of the worlds rangelands are in danger of desertification.
3. Tropical Rain Forest and Human Habitation
a. Deforestation, the removal of trees, has allowed humans to live in areas where forests once covered the land.
b. This land is also subject to desertification; soil in the tropics is often thin and nutrient-poor because all the nutrients are tied up in the trees and other vegetation.
c. People are settling in tropical rain forests following the building of roads.
ii. Water
1. Increasing Water Supplies
a. Dams
i. The world’s 45,000 large dams catch 14% of all precipitation runoff, providing water for up to 40% of irrigated land, and give some 65 countries more than half their electricity.
ii. Damming of certain rivers has been so extensive that they no longer flow as they once did.
iii. Dams have other drawbacks:
1. They lose water due to evaporation and seepage into underlying rock beds.
2. The salt left behind by evaporation and agricultural runoff increases salinity and can make a river’s water unusable farther downstream.
3. Dams hold back less water with time because of sediment buildup.
b. Aquifers
i. To meet freshwater needs, people are pumping vast amounts of water from aquifers, which are reservoirs found just below or as much as 1km below the surface.
ii. They hold about 1000 times the amount of water that falls on land as precipitation each year.
iii. In the past 50 years ground water depletion has become a problem in many areas of the world.
c. Consequences of Groundwater Depletion
i. Removal of water is causing land subsidence, a settling of the soil as it dries out.
ii. Subsidence causes damage to canals, buildings, and underground pipes.
iii. Withdrawal of ground water can cause sinkholes, in which an underground cavern collapses when water no longer holds up its roof.
d. Saltwater Intrusion
i. Is another consequence of aquifer depletion.
ii. The flow of water from streams and aquifers usually keeps them fairly free of saltwater, but as water is withdrawn, the water table can lower to the point that seawater backs up into streams and aquifers.
iii. Saltwater intrusion reduces the supply of freshwater along the coast.
2. Conservation of Water
a. By 2025 two-thirds of the world’s population may be living in countries that are facing serious water shortages.
b. Some solutions for expanding water supplies have been suggested.
c. Planting drought and salt-water tolerant crops have been suggested.
d. Using drip irrigation delivers more water to crops and saves about 50% over the traditional method, while increasing crop yield.
e. Reusing water and adopting conservation measures could help the world’s industries cut their water demand by more than half.
iii. Food
1. Soil Loss and Degradation
a. Land suitable for farming and grazing animals is being depleted worldwide.
b. When bare soil is acted on by water and wind, soil erosion occurs and topsoil is lost. As a result marginal rangeland becomes desertized, and farmland loses its productivity.
c. The custom of planting the same crop in straight rows that facilitates the use of large farming machines has caused the US and Canada to have one of the highest rates of soil erosion in the world.
d. Between 25%-35% of the irrigated western croplands are thought to have undergone salinization. Salinization makes the land unsuitable for growing crops.
2. Green Revolutions
a. About 50 years ago, researchers began to breed tropical wheat and rice varieties specifically for farmers in the LDC’s.
b. The dramatic increase in yield due to the introduction of these new varities around the world was called the green revolution.
c. These plants helped the world food supply keep pace with the rapid increase in word population.
d. Most green revolution plants are called high responders, because they need high levels of fertilizer, water, and pesticides in order to produce a high yield.
e. They create the same ecological problems that modern farming methods do.
f. Genetic engineering
i. Can produce transgenic plants with new and different trait, among them, resistant to both insects and herbicides.
ii. When herbicide resistant crops are planted, weeds are easily controlled, less tillage is needed, and soil erosion is minimized.
iii. Researchers also want to create crops that tolerate salt, drought, and cold.
3. Domestic Livestock
a. In LDC’s, kwashiorkor, caused by severe protein deficiency, is seen in infants and children ages 1-3, usually after a new arrival in the family and the older children are no longer fed milk but starches.
b. In MDC’s, many people have more than enough protein in their diet.
c. Almost two-thirds of US cropland is devoted to producing livestock feed.
d. Typically cattle are range-fed for about four months, and then they are brought to crowded feedlots where they receive growth hormone and antibiotics, while they feed on grain or corn.
e. If livestock eat a large proportion of the crops in the US, then raising livestock accounts for much of the pollution associated with farming.
iv. Energy
1. Nonrenewable Sources
a. Presently about 6% of the worlds energy comes from nuclear power and 75% comes from fossil fuels. Both of these are finite, nonrenewable.
b. It was once predicted that nuclear power would fulfill a significant portion of the world’s energy need’s, this has not happened for 2 reasons:
i. People are very concerned about nuclear power dangers.
ii. Radioactive wastes from nuclear power plants remain a threat to the environment for thousands of years, and we still have not decided how best to safely store them.
c. Fossil Fuels (oil, natural gas, and coal) are so named because they are derived from the compressed remains of plants and animals that died many thousands of years ago.
d. The US makes up only 5% of the world’s population, but it uses more than half of the fossil fuel energy supply.
e. Each person in the MDC’s uses approximately as much energy in one day as a person in an LDC does in one year.
f. Fossil Fuels and Global Climate Change
i. In 1850 the level of carbon dioxide in the atmosphere was about 280 ppm, and today it is about 350 ppm. This increase is due largely to the burning of fossil fuels and the burning and clearing of forests to make way for farmland and pasture.
ii. Human activities are causing the emission of other gases as well, these gases are known as greenhouse gases because they allow solar radiation to pass through but hinder the escape of infrared heat back into space.
iii. The global climate has warmed about 0.6 degrees Celsius, and it may rise as much as 1.5-4.5 degrees Celsius by 2100. If so sea levels will rise as glaciers melt and warm water expands.
iv. Major coastal cities could be threatened. The present wetlands will be inundated and the loss of aquatic habitat will be great, wherever wetlands cannot move inward because of coastal development and levees.
v. Coral Reefs will most likely drown as water levels rise.
vi. On land, regions of suitable climate for various species will shift toward the poles and higher elevations.
2. Renewable Energy Sources
a. Renewable types of energy include hydropower, geothermal, wind, and solar.
b. Hydropower
i. Hydroelectric plants convert the energy of falling water into electricity.
ii. Hydropower accounts for about 10% of the electric power generated in the United States and almost 98% of the total renewable energy used.
iii. Brazil, New Zealand, and Switzerland produce at least 75% of their electricity with waterpower, but Canada is the worlds leading producer.
iv. Worldwide hydropower presently generates 19% of all electricity utilized, but this percentage is expected to rise.
c. Geothermal Energy
i. Elements such as uranium, thorium, radium, and plutonium undergo radioactive decay below the Earth’s surface and then heat the surrounding rocks to hundreds of degrees Celsius.
ii. When rocks are in contact with underground streams or lakes, huge amounts of steam and hot water are produced. This steam can be piped up to the surface to supply hot water for home heating or to run steam-driven turbogenerators.
d. Wind Power
i. Wind power is expected to account for a significant percentage of our energy needs in the future.
ii. A community that generates its own electricity by using wind power can solve the problem of uneven energy production by selling electricity to a local public utility when an excess is available and buying electricity when wind power is in short supply.
e. Energy and the Solar-Hydrogen Revolution
i. Solar energy is diffuse energy that must be:
1. Collected
2. Converted to another form
3. Stored if it is to compete with other available forms of energy
ii. In a Photovoltaic (solar) Cell, a wafer of the electron emitting metal is in contact with another metal that collects the electrons and passes them along into wires in a steady stream.
iii. The photovoltaic cells placed on roofs generate electricity that can be used inside a building or sold back to a power company.
iv. Scientists are working on the possibility of using solar energy to extract hydrogen from water via electrolysis. The hydrogen can then be used as a clean burning fuel: when it burns water is produced.
v. The advantages of a solar-hydrogen revolution are at least twofold:
1. The world would no longer be dependent on the Middle East region for oil.
2. Environmental problems, such as global warming, acid deposition, and smog, would begin to lessen.
v. Minerals
1. Are non-renewable raw materials in the Earth’s crust that can be mined and used by humans.
2. Nonrenewable minerals include fossil fuels; nonmetallic raw materials, such as sand, gravel, and phosphate; and metals, such as aluminum, copper, iron, lead, and gold.
3. Hazardous Wastes
a. The consumption of minerals contributes to the buildup of hazardous wastes, including synthetic organic chemicals, in the environment.
b. The nine most commonly found contaminants of the environment are heavy metals: lead, arsenic, cadmium, chromium, and synthetic organic compounds: trichloroethylene, toluene, benzene, polychlorinated biphenyls, and chloroform.
c. Synthetic organic chemicals play a role in the production of plastics, pesticides, herbicides, cosmetics, coatings, solvents, wood preservatives, and hundreds of other products.
Biodiversity
i. Loss of Biodiversity
1. Biodiversity can be defined as the defined as the variety of life on Earth, described in terms of the number of different species.
2. Habitat Loss
a. Human occupation of the coastline, semiarid lands, tropical rain forests, and other areas has contributed to the loss of biodiversity.
b. Tropical rain forests and coral reefs are a big concern, tropical rain forests have already been reduced from their original 14% of landmass to the present 6%. 60% of coral reefs have been destroyed or are on the verge of destruction; it’s possible that all coral reefs may disappear during the next 40 years.
c. Alien Species
i. Some times called exotics, are nonnative members of an ecosystem.
ii. Humans have introduced alien species into new ecosystems chiefly due to colonization, horticulture and agriculture, and accidental transport.
iii. Alien species that crowd out native species are termed invasive. One way to counteract alien species is to replant native species.
d. Pollution
i. The following types of environmental pollution particularly threaten Biodiversity.
ii. Acid Deposition decimates forests because it causes trees to weaken and increase their susceptibility to disease and insects.
iii. Global Warming, an increase in the Earth’s temperature due to the presence of greenhouse gases in the atmosphere, is expected to have many detrimental effects, such as destruction of coastal wetlands due to a rise in sea levels; loss of habitat due to temperature shifts; and the death of coral reefs if the temperature increases by 4 degrees Celsius.
iv. Ozone Depletion is caused by the release of CFC’s into the atmosphere causes the shield to breakdown, leading to impairment of crop and tree growth and death of plankton that sustain oceanic life.
v. Synthetic Organic Chemicals released into the environment are endocrine-disrupting contaminants that can possible affect the endocrine system and reproductive potential of food species and humans.
e. Overexploitation
i. Occurs when the number of individuals taken from a wild population is so great that the population becomes severely reduced in numbers.
ii. A positive feedback cycle explains overexploitation: the smaller the population, the more valuable its members, and the greater the incentive to exploit the few remaining organisms.
f. Disease
i. Wildlife is subject to emerging diseases just as humans are. Exposure to domestic animals and their pathogens occurs due to the encroachment of humans on wildlife habitats.
ii. Animals not ordinarily encountered can also infect wildlife.
ii. Direct Value of Biodiversity
1. Medicinal Value
a. Most of the prescription drugs used in the US were originally derived from living organisms.
2. Agricultural Value
a. Crops such as wheat, corn, and rice are derived from wild plants that have been modified to be high producers.
b. The same high-yield, genetically similar strains tend to be grown worldwide. When a virus was devastating rice crops in Africa, researchers grew wild rice plants from thousands of seed samples until they found one that contained a gene for resistance to the virus.
c. Biological pest controls- natural predators and parasites- are often preferable to using chemical pesticides.
3. Consumptive Use Value
a. There has been much success cultivating crops, keeping domesticated animals, growing trees in plantations, and so forth.
b. So far, aquaculture, the growing of fish and shellfish for human consumption, has contributed only minimally to human welfare.
iii. Indirect Value of Biodiversity
1. Waste Disposal
a. Decomposers break down dead organic matter and other types of wastes to inorganic nutrients that are used by the producers within ecosystems.
b. If it were not for decomposition, waste would soon cover the entire surface of our planet.
c. It is less expensive and more efficient to water plants and trees with partially treated wastewater and let soil bacteria cleanse is completely.
d. Biological communities are also capable of breaking down and immobilizing pollutants, such as heavy metals and pesticides that humans release into the environment.
2. Provision of Freshwater
a. Few terrestrial organisms are adapted to living in a salty environment- they need freshwater.
b. The water cycle continually supplies freshwater to terrestrial ecosystems.
c. Unlike other commodities, there is no substitute for freshwater. Salt can be removed from seawater to obtain freshwater but the cost of desalination is about 4 to 8 times the average cost of freshwater acquired via the water cycle.
d. Forests and other natural ecosystems exert a sponge effect. They soak up water and then release it at a regular rate. When rain falls in a natural area, plant foliage and dead leaves lessen its impact, and the soil slowly absorbs it, especially if the soil has been aerated by organisms. The water-holding capacity of forests reduces the possibility of flooding.
3. Prevention of Soil Erosion
a. Intact ecosystems naturally retain soil and prevent soil erosion. Most coastal ecosystems are not as bountiful as they once were because of deforestation and a myriad of other assaults.
4. Biochemical Cycles
a. When human activities upset the usual workings of biochemical cycles, dire environmental consequences include the release of excess pollutants that are harmful to us.
b. Technology is unable to substitute for any of the biogeochemical cycles.
5. Regulation of Climate
a. At the local level trees provide shade and reduce the need for fans and air conditioning during the summer months.
b. Globally forests ameliorate the climate because they take up carbon dioxide. When trees are cut and burned carbon dioxide is released into the atmosphere.
c. Carbon dioxide makes a significant contribution to global warming.
Working Toward a Sustainable Society
i. Today’s Unsustainable Society
1. The population growth in the LDC’s creates an environmental burden, as does the excessive resource consumption of the MDC’s.
2. Both overpopulation by the LDC’s and overconsumption by the MDC’s accounts for the increasing amount of worldwide pollution and the extinction of wildlife observable today.
3. A considerable proportion of land is being used for human purposes. Agriculture uses large inputs of fossil fuels, fertilizer, and pesticides, which create much pollution.
4. More freshwater is used in agriculture than in homes.
5. Our society primarily utilizes nonrenewable fossil fuel energy, which leads to global warming, acid deposition, and smog.
6. LDC’s will soon have increased needs for energy, and therefore it is imperative for the MDC’s to develop renewable energy sources.
ii. Characteristic of a Sustainable Society
1. A natural ecosystem makes use of only renewable solar energy, and its materials cycle through the various populations back to the producer once again.
2. If we want to develop a sustainable society we too should use renewable energy sources and recycle materials, and we should protect natural ecosystems that help sustain our modern society.
3. Rural Sustainability
a. In rural areas we should put an emphasis on preservation.
b. Some other possible ways to help make rural areas sustainable
i. Plant cover crops to stabilize the soil between rows of cash crops or between seasonal plantings of cash crops
ii. Use multiuse farming by planting a variety of crops and use a variety of farming techniques to increase the amount of organic matter in the soil.
iii. Replenish soil nutrients through composting, organic gardening, or other self-renewable methods.
iv. Use low flow or trickle irrigation, retention ponds, and other water conserving methods.
v. Increase the planting of cultivars, which are resistant to blight, rust, insect damage, salt, drought, and encroachment by noxious weeds.
vi. Use precision farming techniques that rely on accumulated knowledge to reduce habitat destruction, while improving crop yields.
vii. Use integrated pest management, which encourages the growth of competitive beneficial insects and uses biological controls to reduce the abundance of a pest.
viii. Plant a variety of a species to reduce our dependence on traditional crops.
ix. Plant multipurpose trees with the ability to provide numerous products and perform a variety of functions
x. Maintain and restore wetlands, protect deltas from storm damage.
xi. Use renewable forms of energy
xii. Support local farmers, fisherman, and feed stores.
4. Urban Sustainability
a. More and more people are moving to a city, resources need to be shared in a way that will allow urban sustainability.
b. Here are some other possible ways to help make a city sustainable.
i. Design an energy efficient transportation system to rapidly move people about.
ii. Use solar or geothermal energy to heat buildings; cool them with an air-conditioning system that uses seawater; and in general use conservation methods to regulate the temperature of buildings.
iii. Utilize green roofs- a wild garden of grasses, herbs, and vegetables on the top of buildings- to assist temperature control, supply food, reduce the amount of rainwater runoff, and be visually appealing.
iv. Improve storm-water management by using sediment traps for storm drains, artificial wetlands, and holding ponds. Increase use of porous surfaces for walking paths, parking lots, and roads. These surfaces reflect less heat, while soaking up rainwater runoff.
v. Instead of traditional grasses, plant native species that attract bees and butterflies and require less water and fertilizers.
vi. Create greenbelts that suit the particular urban setting. Include plentiful walking and bicycle paths.
vii. Revitalize old sections of a city, before developing new sections.
viii. Use lighting fixtures that hug the walls or ground and send light down; control noise levels by designing quiet motors.
ix. Promote sustainability by encouraging recycling of business equipment; use low maintenance building materials, rather than wood.
iii. Assessing Economic Well-Being and Quality of Life
1. The Gross National Product (GNP) is a measure of the flow of money from consumers to businesses, in the form of goods and services purchased.
2. When calculating GNP, economists do not necessarily consider whether an activity is environmentally or socially harmful.
3. Measures that include non-economic indicators are most likely better at revealing our quality of life than is the GNP. The index of Sustainable Economic Welfare (ISEW) includes real per capita income, distributional equity, natural resources depletion, environmental damage, and the value of unpaid labor. ISEW does take into account other forms of value, beyond the purely monetary value of goods and services, as does the GNP.
4. Another index used is the Genuine Progress Indicator (GPI). This indicator attempts to consider the quality of life, an attribute that does not necessarily depend on worldly goods.
5. Economists are searching for a way to measure the following values:
a. Use Value: actual price we pay to use or consume a resource, such as the entrance fees into national parks.
b. Option Value: preserving options for the future, such as saving wetland or a forest.
c. Existence Value: saving things we might not realize exist yet, such as flora and fauna in a tropical rain forest that, one day, could be the source of new drugs.
d. Aesthetic Value: appreciating an area or creature for its beauty and/or contribution to biodiversity.
e. Cultural Value: factors such as language, mythology, and history that are important for cultural identity.
f. Scientific and Educational Value: valuing the knowledge of naturalists, or even an experience of nature, as types of rational facts.
6. Development of the environment will always continue, but perhaps we can use these values to help us direct future development.
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