Patterns in Nature

PATTERNS IN NATURE

REVIEW QUESTIONS

ANSWERS

a. MULTIPLE CHOICE

1) b. 2) d. 3) c.; the electron microscope uses a magnetic lens to focus electron beams 4) d.; animal cells possess vacuoles, although these are not usually permanent structures 5) a. 6) c.; carbohydrates such as chitin in insects provide structural support 7) d. 8) a.; fats can in fact dissolve in the membrane's hydrophobic lipid layer and pass through it 9) d. 10) c. 11) d. 12) c. 13) b. 14) c. 15) a.

b. SHORT ANSWER AND LONGER RESPONSE QUESTIONS

16) a. In closed circulatory systems the blood is completely contained in the blood vessels. Open circulatory systems, such as those found in molluscs and insects, also have special air spaces (haemocoels) that transport blood around the body. b. Mammals have a closed circulatory system in which the heart pumps blood through three types of blood vessel: arteries, capillaries and veins. Insects have an open circulatory system that includes blood vessels and haemocoels. Note that the blood in insects does not carry oxygen around the body. This job is instead done by the tracheae, a system of tubes.

17) a. Multicellular organisms need efficient transport systems so that all the cells of the body can be supplied with food and oxygen and wastes from each cell can be removed. b. Water and minerals move through the plant in the xylem, a series of non-living, woody vessels. Organic materials move around the plant in the phloem, a series of living cells composed of sieve tubes and companion cells. c. The major driving force responsible for the continuous upward movement of water and minerals in the xylem is the evaporation of water from the stomata in the leaves in the process of transpiration. This upward movement is also helped by the cohesive forces between the water molecules, adhesive forces between water molecules and the walls of the xylem vessels, and capillarity (the tendency for water to move unassisted to certain heights up narrow tubes). Movement of organic material in the phloem relies mainly on osmotic pressure differences between 'sources' and 'sinks', although active transport is used to initially move materials from the leaves into the phloem. PATTERNS IN NATURE

REVIEW QUESTIONS

ANSWERS

18) The effect of humidity on transpiration can be studied by placing a leafy geranium shoot in a measuring cylinder containing 50 ml water with a layer of oil on the top. Another shoot can be prepared in the same manner, but this time with a plastic bag tied around the leaves to increase the humidity in the air around them. Both sets of apparatus are then left for 24 hours and the volume of water that has been lost from each is recorded.

19) Autoradiography can been used to trace the sugars produced in photosynthesis to the phloem tissue in plants. In this procedure, the plants are exposed to carbon dioxide containing radioactive carbon 14, then cut into fine sections and pressed against X-ray film. Observation of the film reveals that the sieve tubes within the phloem are darkened, therefore suggesting that sugars are carried through the plant in these vessels.

20) Rabbits are herbivores and therefore need to break down large amounts of cellulose. The caecum contains large numbers of bacteria that can digest cellulose, and therefore needs to be quite long. The colon also needs to be long so that it can process the extensive amounts of faecal matter produced as a by-product of cellulose digestion.

21) a. animal cell; b. plant cell; c. cytoplasm; d. nucleus; e. cell membrane; f. chloroplast; g. cell wall; h. vacuole

22) Muscle cells require more energy, and so would be expected to carry out more respiration. As a result, we would expect to find a higher density of mitochondria in these cells as their primary function is to carry out respiration.

23) Class of organic compound Elements/molecules present Function of compound in cell carbon, hydrogen, oxygen, nitrogen, growth and repair of body tissues, proteins sometimes phosphorous and present in hormones, cell sulphur membranes and enzymes major source of energy for the cell; cellulose and chitin are structural carbohydrates carbon, hydrogen and oxygen carbohydrates found in cell walls and insect exoskeletons/fungal cell walls, respectively fats and oils are energy storage molecules, steroids are present in carbon, hydrogen and oxygen; less lipids membranes and hormones, waxes oxygen than in carbohydrates act as a waterproof layer in leaves and fruits main component of DNA, the ribose or deoxyribose sugar, molecule responsible for heredity, nucleic acids phosphate group and nitrogen base and RNA, which is involved in the manufacture of proteins

PATTERNS IN NATURE REVIEW QUESTIONS

24) e.g. Testing for glucose in cells: Use a mortar and pestle and a small amount of water to mash up samples of peas, potato, onion and celery. Place 2ml Benedict's solution and about 1 ml of the mixture to be tested in a test tube. Heat the tube gently over a Bunsen burner. If glucose is present, the mixture should turn from blue to orange. Glucose should be present in varying degrees in each sample, as it is used for respiration in the mitochondria of all cells.

25) a. Diffusion occurs when substances move from where there is a greater amount of them to where there are less of them. Osmosis is the diffusion of water molecules across a differentially permeable membrane. This means that water, but not certain solutes, can move across the membrane, with the result that water diffuses from a low solute concentration to a high solute concentration. 26)

direction of water movement (from a low solute concentration to a high one) 27) i) Rainforest plants have broad, flat leaves with evenly distributed palisade cells. Leaves are broad so that the surface area exposed to the sun is maximised; palisade cells are evenly distributed so that light from all angles can be utilised; ii)Marine algae are thin, with a reduced number of cell layers to allow water and dissolved gases to diffuse quickly to all parts of the plant. Chloroplasts are found throughout the plant so that the limited available light can be utilised efficiently; iii) Cactus plants often have leaves that are reduced to spines, which reduce the surface area of the leaf and therefore helps to reduce evaporative water loss through the stomata. In many cases, the stem takes over the role of photosynthesis in this type of plant; iv) Stomata in the water lily are located on the upper surface of the leaf to maximise carbon dioxide uptake from the air. Leaves are broad and flat to increase the surface area exposed to the sunlight and the air, and to assist buoyancy.

28) Teeth help to break food into smaller pieces, which gives the food a greater surface area. This means that it can be acted on more rapidly by digestive enzymes. Incisors are cutting teeth, canines are used for stabbing and tearing food and molars are used for grinding.

29) Materials needed: junket tablets (these contain the enzyme, rennin, which coagulates milk), test tubes, milk, mortar and pestle Procedure: 10 ml milk was poured into each of two test tubes. Both tubes were immersed in a water bath at 37°C. A whole junket tablet was placed in one of the tubes and a crushed tablet was placed in the other tube. Both tubes were observed over the next few minutes. Results: The milk with the crushed tablet in it was found to coagulate first. Conclusion: These results indicate that increasing the surface area of a reactant helps to increase the reaction rate. PATTERNS IN NATURE

REVIEW QUESTIONS

30) a. Mitosis, or cell division, is essential for the growth and repair of organisms. b. The diploid number of an organism is the full number of chromosomes within the nucleus. In humans, the diploid number is 46. c. a. interphase: the nuclear material (DNA) is duplicating itself; b. prophase: the chromosomes are visible; c. metaphase: the chromosomes line up across the centre of the cell along the spindle; d. anaphase: the individual chromatids of each chromosome move apart; e. telophase: two new nuclei form around the separated chromatids; cytokinesis: the cytoplasm also divides, resulting in two new cells