Biology Unit

A punnett square is a two by two square which is used to predict the possible phenotypes of offspring, and its ratio. (Krough)

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b) The male and female gametes contain only one set of alleles. (Krough)

c) The genes of the parents go on the outside of the boxes. (Krough)

d) The possible gene outcome from the parental genes goes inside the boxes. (Krough)

e) The punnett square always contains only 4 boxes or squares, that is, two rows and two columns. (Krough)

a) The Law of segregation is based on Mendel’s pea plant experiment where he came to the conclusion that alleles for a trait separate when gametes are formed and are randomly paired at fertilization, after which one allele is expressed dominantly while the other is masked. (Krough)

b) Law of independent assortment states that alleles separate independently during gamete formation, which means that traits are inherited by offspring independently of each other.

c) It allows us to predict the progeny phenotypes. (Krough)

3. a) Test cross is an experimental cross of an individual organism with dominant phenotype (but unknown genotype) with an organism with a known homozygous recessive phenotype and genotype. (Krough)

b) A test cross is used to determine an organisms genotype. (Krough)

c) An organism with a dominant phenotype (but unknown genotype) is crossed with an organism with a known homozygous recessive phenotype and genotype. (Krough)

d) If only fifty percent of the offspring are reflecting one phenotype, whereas the other fifty percent is reflecting the other phenotype, the unknown genotype is a heterozygous dominant, for example, Bb. If all the progeny are reflecting only the dominant phenotype, then the unknown genotype is a homozygous dominant, for example, BB. (Krough)

4. a) The purpose of pre-natal diagnostic testing is to monitor fetal growth and development, lung maturity and to check chromosomal abnormalities in order to enable early medical intervention and prenatal counseling. (Krough)

b) This technique sends high frequency sound waves which are reflected to different degrees by body organs. These waves are measured and displayed on a screen. (Krough)

c) In amniocentesis, a thin needle is passed through the abdomen and a sample of amniotic fluid is collected. (Krough)

d) After administering local anesthesia, chorionic villus sampling is performed by passing a catheter through the cervix or a needle through the abdomen to collect a sample of the placenta. (Krough)

5.a) If organisms were made independently, their distribution across the globe would also be independent. Biogeography tells us that genetically similar species are not distributed evenly, hence proving the evolutionary theory. (Krough)

b) The occurrence of homologous structures within different species provides strong evidence that individual species were formed as a result of divergence from a common ancestor. (Krough)

c) The biochemistry of different species is closely related, providing evidence of decent from a common ancestor. (Krough)

6.a) Natural selection is the process by which only organisms fit to survive in a particular environment survive long enough to pass their traits to their offspring, thus increasing in number. (Krough)

b) Organisms best adapted to survive, in a particular environment, are preferentially selected by the environment they live in. (Krough)

c) The sickle cell trait in Africa has a protective role against malaria. People heterozygous for the disease are preferentially selected since it protects them against malaria with minimal effects of the disease itself. People homozygous for the disease are protected from malaria but they do not survive long enough due to the effects of the disease. People without the gene, are exposed to the fatal effects of malaria in the region. (Krough)

7.a) Genetic drift, gene flow, mutation, non-random mating and natural selection (Krough)

b) Genetic drift: genetic drift affects a population’s gene pool but unlike natural selection, it does not help in adaptation. (Krough)

Gene flow: it may cause a difference in the allelic frequency of a particular trait. It can also add new alleles to the gene pool. (Krough)

Mutation: mutations can be either beneficial or harmful. Beneficial mutations can be naturally selected, thus adding to the gene pool. (Krough)

Non-random mating: non-random mating minimizes the chance of gene diversification. (Krough)

Natural selection: this phenomenon allows the transfer of useful alleles, necessary for survival, to their progeny. (Krough)

8.) Gene mutations cause a change in the codon sequence, which may prematurely inhibit any further addition of amino acids or may code for a different amino acid. This changes the end product forming a completely new protein, hence producing gene variation.

The cross over process in sexual recombination also allows formation of gene combinations in the offspring, hence increasing genetic variation. (Krough)

9.) Pre-zygotic and post-zygotic barriers are the two kinds of reproductive barriers. Reproductive barriers prevent species from producing fertile or viable offspring, which prevents speciation. (Krough)

10.a) A localized group of individuals that belong to the same species are called population. (Krough)

b) Species are a group of populations that can interbreed and produce viable offspring. (Krough)

c) A population is the smallest unit that can evolve. (Krough)

11.) On land, organisms must be able to conserve water, exchange gasses, have a support system to support their body weight and balance, must have a conduction system and must be ale to reproduce. (Krough)

12.a) Humans evolved from ape like ancestors. (Krough)

b) Prosimians are mammals that are primates. Monkeys and apes are excluded in this classification. (Krough)

c) Anthropoids are creatures that have both human and animal characteristics. (Krough)

d) The human ancestral line is the hominid family. (Krough)

e) Man has greater intelligence and a developed sense of speech and understanding, unlike apes and monkeys. Other than these minor differences, monkeys, apes and men have great similarities in their anatomical structures and emotional feelings. (Krough)

13.) Early humans were able to dominate every territory they occupied. Through scavenger-gathering and hunting, they would sometimes over hunt animals often destroying the balance of the food chain in a particular community. Through times, as agriculture dominated as the main source of food, vast areas of forests were cleared, caused destruction of many wildlife habitats. Pesticides and insecticides used caused bioaccumulation of toxic substances in the food chain. Eventually, the machine age dominated and more land was needed for industrialization, urbanization and agriculture. This has greatly decreased the area of forested land, causing many animals to be at the verge of extinction. (Krough)

14. a) Energy flow and chemical cycle: flow of energy through the food chain starts in the form of sunlight which the plants and other photosynthetic organisms use to convert to chemical energy, used by other organisms. The passage of energy through the components of the ecosystem is known as energy flow. The reuse of chemical energy within the ecosystem is known as the chemical cycle. (Krough)

b) Community and ecosystem: community is a set of populations that inhabit a particular area. Ecosystem consists of a community along with its physical and chemical factors that make up its non-living environment. (Krough)

c) Habitat and ecological niche: a specific place occupied by an organism is known as its habitat. Ecological niche is the relationship of the organism to its environment or habitat. (Krough)

d) Co -evolution and symbiosis: co evolution is an evolutionary change in which one species acts as a selective force on the second species which as a result, adapts to this force in turn causing a selective force on the first species as well. Symbiosis is a beneficial association between two organisms that allow each other to survive or thrive. (Krough)

15. a) Competition: An interaction between two organisms for resources. (Krough)

b) Predation: An interaction between organisms, in which one organism feeds on the other. (Krough)

c) Mimicry: Resemblance of organisms to other organisms or to their environment thus protecting them from their predators. (Krough)

d) Symbiosis: Beneficial interaction between two organisms that help each other to survive or thrive in an environment. (Krough)

16. a) A keystone species is one that plays an important role in the maintenance of the structure of that community and whose impact would be greater than expected based on its relative abundance and total biomass. (Krough)

b) A keystone species is important for the survival of other species in that community. If a keystone species is made to disappear, other species will also be driven to extinction. (Krough)

17.a) Community succession is the process by which an ecosystem can renew itself to form a stable community. For example, any form of destruction, such as volcanoes or human intervention, the ecosystem undergoes a process, where by it can return to its previous structure. (Krough)

b) A climax community consists of plants and animals, which through the process of ecological succession has reached a steady state. (Krough)

c) For instance, if this community is destroyed because of human destruction of trees, eventually the plants will re-grow over a period of time until it reaches the climax stage, after which it will become stable. (Krough)

18.a) Green plants form the first tropic level (producers), herbivores form the second (primary consumers) and the carnivores form the third and the forth level (secondary and tertiary consumers). (Krough)

b) Energy captured by plants from the sun is converted to chemical energy, which is transferred to the herbivores and carnivores down the food chain. (Krough)

c) The ecological pyramid consists of producers, primary consumers, secondary consumers, tertiary consumers and quaternary consumer. The amount of energy drops by ninety percent as it passes to the next tropic level of the pyramid. (Krough)

19.) Ecology is the study of organisms and the environment in which they live. (Krough)

20.) If a graph is plotted with population size against time for a population that is growing exponentially, a J. shaped curve is displayed. When this population grows at a rate that limits the resources needed by this population, the rate of growth slows down, demonstrating an S. shaped graph. (Krough)

21.) Equilibrial species have a slower maturation rate, reproduce relatively late and have fewer offspring per reproductive cycle. Their population size does not exceed the carrying capacity of their habitat, unlike opportunistic species, which mature and reproduce earlier and have lesser life spans than equilibrial specie. (Krough)

22. a) In a stable population, the population size of almost all age groups are the same. If the growth rate is explosive, the size of the lower age groups will be the greatest. (Krough)

Illiteracy, early age at marriage, the need for a greater labor force in farms and disease are some factors that influenced human population growth in the past. (Krough)

b) At present, education and other factors delaying early marriage, use of contraception and better health care are factors that influence population growth at present. (Krough)

24.) Human overpopulation means earlier extinction of available resources, vast deforestation and environmental pollutions. (Krough)

25.) Causes for loss of biodiversity on the planet are the following: Habitat destruction, dumping of solid wastes, greenhouse effect, overpopulation, pesticide use, over hunting and over harvesting. (Krough)

26.) Biological magnification is the process whereby toxins and chemicals accumulate successively at higher levels in the food chain. When a predator feeds on its prey, it accumulates all the toxins from its food and since the top carnivore accumulates most of the toxins in the food chain, it falls as the usual victim to its effects. (Krough)

27.) Deforestation and industrialization are two major factors that effect the environment around us. Other factors, such as overhunting a specific species for human benefit, such as elephants for its tusks, and over breeding of others, such as herds for human consumption, also affect the ecosystem by altering the food chain. (Krough)


Krough, David. Biology: A Guide to the Natural World. 5th. Benjamin Cummings, 2010. Print.

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