Unit 2 Revision questions and answers: the variety of living organisms

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1. What is intraspecific variation?

2. What does standard deviation tell you about a dataset?

3. Why are identical twins not perfectly identical?

4. What are the three constituents of a nucleotide?

5. Which base does C pair with?

6. The triplet code is degenerate. What does this mean?

7. What are introns?

8. How is DNA arranged in a prokaryotic cell?

9. Give two ways in which meiosis leads to genetic variation.

10. What is a genetic bottleneck?

11. How does the founder effect reduce genetic diversity?

12. Explain the advantage of the oxygen dissociation curve being shifted to the right in small mammals such as mice.

13. Why does carbon dioxide cause the oxygen dissociation curve to shift to the right?

14. What monomer is cellulose made of?

15. Contrast the structures of cellulose and starch and explain how these different structures allow them to act as structural and storage molecules respectively.

16. What do thylakoids contain, and what is its purpose?

17. What is the role of DNA helicase in DNA replication?

18. Name the four subphases of mitosis in order.

19. What is the role of the centromere in mitosis?

20. What happens during interphase?

21. What is an organ?

22. How does the countercurrent exchange system allow efficient gas exchange in fish?

23. Describe how the structure of a leaf is adapted for gas exchange.

24. Name two structures involved in gas exchange in insects.

25. Give two ways in which xerophytic plants are adapted to limit water loss.

26. Name the blood vessel which goes out of the liver back towards the heart.

27. Explain why arteries have a thicker elastic tissue layer than veins.

28. Explain why arterioles have a thicker muscle fibre layer than arteries.

29. Explain the importance of plasma proteins in the reabsorption of tissue fluid.

30. Give two ways in which tissue fluid is returned to the circulatory system.

31. Give two differences between the apoplast and the symplast pathway.

32. What is the role of casparian strips?

33. Explain how water moves up stems.

34. Give three factors which affect transpiration rate.

35. What is a phylogeny?

36. Name the taxonomic group between phylum and order.

37. Describe how DNA hybridisation can be used to determine the relationship between organisms.

38. What is the importance of courtship in mating?

39. Describe how the frequent use of antibiotics leads to antibiotic resistance in bacteria.

40. What is vertical gene transmission?

41. Describe the events that occur in horizontal gene transmission.

42. Give two ways in which agricultural practices can reduce species diversity.

43. Why is Simpson’s index of diversity a better measure of species diversity than simply counting the number of species?

1.

Variation between individuals of the same

species (within a species)

2.

The spread of the data about the mean

3.

There is variation due to environmental factors

4.

Nitrogen-containing base, deoxyribose and

phosphate group

5.

T

6.

Multiple codons may encode the same amino acid

7.

Non-coding sections of genes

8.

Circular chromosome and plasmids

9.

Crossing over between homologous chromosomes

during prophase I; independent segregation of chromosomes during anaphase I

10.

A sudden large decrease in a population due to a

chance event

11.

Small number of individuals have a very limited

gene pool; breeding occurs but successive generations have a small variety of

alleles, so genetic diversity is low

12.

Small mammals have a large SA:volume ratio so

lose heat easily; right-shifted oxygen dissociation curve means reduced

affinity of Hb for oxygen, so oxygen is more readily unloaded at low pO2s,

i.e. at respiring tissues, for respiration to release energy to keep the body

warm

13.

Lowers pH

of blood; Hb acts as a buffer, accepting protons which causes it to change

shape and lowers its oxygen affinity (the Bohr effect)

14.

Beta-glucose

15.

Cellulose is a straight-chain, allowing it to be

packed into microfibrils and macrofibrils with hydrogen bonds between adjacent

chains, which gives it tensile strength, making it ideal for support and

structure of plant cell walls. By contrast starch is branched, allowing it to

be more easily hydrolysed as enzymes can operate on all ends of the branches,

and is coiled and compact so that a lot of it can fit into a small space (i.e.

starch grains), making it ideal for energy storage.

16.

Chlorophyll, which traps light energy for

photosynthesis

17.

Separates the double helix by breaking hydrogen

bonds, allowing new bases to be added onto the template strands

18.

Prophase, metaphase, anaphase, telophase

19.

The centromere holds chromatids together and

attaches them to opposite ends of the spindle. At anaphase it allows them to

split and move towards opposite ends of the spindle.

20.

Growth of the cell; synthesis of new organelles;

replication of DNA; regular checkpoints to prevent the cell from dividing

uncontrollably

21.

Different types of tissues coordinated to carry

out a function or variety of functions

22.

Blood and water flow in opposite directions, so

a concentration gradient of oxygen is maintained at all points along the gill

lamellae and thus the maximum amount of oxygen can diffuse from the water into

the blood.

23.

Stomata allow gases to diffuse in and out; air

spaces between spongy mesophyll cells maximise surface area for diffusion

24.

Spiracles, tracheae, tracheoles (any two)

25.

Thin leaves with a small surface area; sunken

stomata trap water vapour; hairs trap water vapour; waterproof waxy cuticle

stops water passing through

26.

Hepatic vein

27.

Elastic tissue smooths out blood pressure; blood

in arteries at higher pressure than in veins

28.

Muscle contracts to constrict lumen and control

blood flow; arterioles connect to capillaries which are much smaller in volume,

so lumen must be constricted more

29.

Soluble so lower the water potential of the

blood, causing water to move from the surrounding tissues into the capillaries

by osmosis

30.

Reabsorption into capillaries; drainage into

lymph vessels/lymphatic system

31.

Apoplast is through cell walls whereas symplast

is through cytoplasm/vacuoles; in apoplast pathway water moves due to cohesion

between molecules but in the symplast pathway it moves by osmosis; apoplast

pathway prevented by Casparian strips/stops at endodermis but symplast

unaffected by Casparian strips (any two)

32.

Waterproof so force water in apoplast pathway

into the symplast pathway at the endodermis

33.

As water enters the xylem by osmosis the root

pressure created forces water slightly up the xylem. Water vapour diffusing out

through the stomata causes water to move from the xylem into mesophyll cells by

osmosis, creating a pull on the continuous column of water in the xylem due to

intermolecular cohesion. Adhesion between water and the xylem walls also pulls

water molecules upwards.

34.

Humidity, wind speed, temperature, light (any

three)

35.

Organisms grouped according to evolutionary

history/lineage

36.

Class

37.

Single strand of DNA from two organisms fused to

form a hybrid and then heated to break hydrogen bonds until the strands

separated. The greater the sequence identity (i.e. the closer related the

organisms) the more hydrogen bonds form between complementary base pairs and

thus the closer the evolutionary relationship.

38.

Allows an individual to recognise a mate of the

same species, synchronises fertility and stimulates production/release of

gametes

39.

Mutation occurs in one bacterium giving it an

allele for antibiotic resistance. Antibiotics kill the non-resistant bacteria

but surviving bacteria survive and reproduce, passing on the allele by vertical

gene transmission so that the frequency of the allele in the population

increases. Horizontal gene transmission by conjugation may occur between

bacteria of different species.

40.

The passing on of genes by asexual reproduction

(binary fission)

41.

Conjugation tube/pilus extends from donor

bacterium and fuses with recipient bacterium; plasmid is replicated and moves

through the pilus into the recipient.

42.

Monoculture causes a large area of land to be

dominated by a single species; pesticides kill insects and other animals

(disrupting food webs); forest cleared, hedgerows chopped down and wetlands

drained – less variety of habitats and food sources for animals; deforestation

leads to fewer plant species and machinery may kill animals; eutrophication

disrupts aquatic ecosystems; predators culled due to their impact on livestock

(any two)

43.

Simpson’s index of diversity takes into account

the number of organisms of each species, which is important as an ecosystem may

have many species but could be dominated by just one or two and thus have a low

index of diversity.

Questions

answers