EXAM QS - SURVIVAL AND RESPONSE

• IAA is a specific growth factor.

  (a)     Name the process by which IAA moves from the growing regions of a plant shoot to other tissues. (1)?

  Diffusion
• When a young shoot is illuminated from one side, IAA stimulates growth on the shaded side. Explain why growth on the shaded side helps to maintain the leaves in a favourable environment?

  Causes plant to grow/ bend towards light (positive phototropism)

  Light is required for photosynthesis
• NAA is a similar substance to IAA. It is used to control the growth of cultivated plants. Plant physiologists investigated the effect of temperature on the uptake of NAA by leaves. They sprayed a solution containing NAA on the upper and lower surfaces of a leaf. The graph shows their results.

   

  (c)     Explain the effect of temperature on the rate at which NAA is taken up by the lower surface of the leaf. (2)?

  • As the temperature increases the rate of NAA uptake increases
  • DUE to more kinetic energy/ faster movement of molecules
  • SO more diffusion occurs
• There are differences in the properties of the cuticle on the upper and lower surfaces of leaves.

  (i)      Suggest how these differences in the cuticle might explain the differences in rates of uptake of NAA by the two surfaces. (2)?

  Thicker cuticle on upper surface and thinner on the lower surface

  SO more diffusion and shorter diffusion on lower surface
•   In this investigation, the physiologists investigated the leaves of pear trees.

  Explain why the results might be different for other species.(1)?

  Different species have different properties e.g cuticle thickness, or number of stomata, or LEAF size
• Scientists investigated the effect of relative humidity on the activity of woodlice. They set up a Petri dish as shown in Figure 1.

  In the bottom half they put a substance which absorbs water. Different concentrations of this substance produced different humidities in the air above the mesh.

  The movement of the woodlice in low relative humidity is an advantage to their survival.Explain how. (2)?

  Low relative humidity results in more woodlice moving so increased chance of leaving dry and unfavourable environment
•   When one unit of light energy falls on cell 3, no light is seen. But, when one unit of light energy falls on cell 3, one unit falls on cell 4 and one unit falls on cell 5, light is seen.?


  One Unit does not meet threshold, 3 units do meet threshold and can allow depolarisation for an action potential/ impulse

  Spatial summation/ sufficient neurotransmitter released from 3 receptors
• Cells of the same type as cells 6 and 7 are found in large numbers at the fovea. This results in colour vision with high visual acuity.

  Explain what causes vision using the fovea.

  TO BE IN COLOUR?

  3 different types of cone cells, type 6 and 7 are sensitive to different wavelengths
• Cells of the same type as cells 6 and 7 are found in large numbers at the fovea. This results in colour vision with high visual acuity.

  Explain what causes vision using the fovea.

  TO HAVE HIGH VISUAL ACUITY?

  Impulses run along separate bipolar cells

  EACH receptor cell connects to a separate neurone
• Nocturnal mammals are active at night. Describe how the number and distribution of rods and cones across the retina would differ in a nocturnal mammal from the number and distribution in a human. Explain your answer (3)?

  More rods, fewer cones in nocturnal mammals compared to in human.

  Rods at fovea

  Rods have high sensitivity/ retinal convergence

  Rhodopsin bleached at low light intensities
• Use your knowledge of indoleacetic acid (IAA) to explain the growth curvature shown in Figure 1. (3)?

  Tip Produces IAA

  IAA diffuses into shoot

  More elongation of cells on one side
• Using the procedure in Figure 2 and the calibration curve in Figure 3, describe how you could compare the IAA concentration in shoot tips from two different plant species. In your answer you should refer to all the variables that should be controlled to produce a valid comparison. (5)?


  You can compare through the:

  • sizes of shoots/tips
  • number of shoots/ tips
  • sizes/ types of agar blocks
  • compare the shoots at the same stage of growth and development
  • time period they are kept on agar
  • Temperature they are kept in
• Name the type of behaviour shown by beetles G, J, P and R, and suggest one advantage to adult beetles of the type of behaviour shown. (2)?

  BEHAVIOUR: Positive photo taxis

  ADVANTAGE: To avoid any potential predators/ to avoid competition/ to find a mate
• Explain why the student removed the shoot tip from each seedling. (2)?

  Tip produces IAA

  So would impact the IAA concentration being measured
• Explain why the student added glucose solution to each Petri dish?

  For respiration

  To provide ATP/ energy for growth
• Explain why the lids were kept on the Petri dishes?

  To prevent evaporation

  Which will alter the concentration of IAA solution or alters the water potential
• Describe and explain the results shown in Table 1 above and suggest how the results might have differed if lengths of root had been used (3)?

  Increase in IAA the higher the mean change in length

  High IAA stimulates cell elongation - which occurs in shoots

  IN ROOTS - growth/ cell elongation is inhibited
• The student produced the different concentrations of IAA using a stock 1 g dm−3 solution of IAA (1 g dm−3 = 1 part per thousand) and distilled water. Complete Table 2 with the volumes of stock IAA solution and distilled water required to produce 40 cm3 of 10 ppm (parts per million) IAA solution. (1)?

  C1V1=C2V2

  C1 = 1ppt

  V1= 40

  c2=10

  V2?

  • WORK OUT V2
  • ANS = 0.04 and 39.6
• Suggest two advantages of simple reflexes. (2)?

  Rapid

  Protect against damage to body tissues

  Does not have to be learnt

  Help escape from predators/ harm

  Enables homeostatic control
• Give one similarity and one difference between a taxis and a tropism. (2)?

  Similarity: Both are directional responses to a stimulus Difference: Taxis the organism moves, while tropism is a growth response.
• What do these results show about the responses of the roots of tomato plants to gravity and salt? (3)

  Growth in direction of gravity

  Grow away from Salt

  Salt has more effect than gravity
• Explain why this root tip would grow away from salt?

  More carriers in cell L

  So less IAA in cell L and more in R

  SO more elongation in L and less cell elongation in R
• The biologist concluded that the worms’ behaviour demonstrated taxis. How do these results support this conclusion?

  Taxis is movement away or towards a stimulus

  and the worms move towards the temperatures they were cultured at
• Using the information provided, suggest an explanation for the worms’ behaviour on the glass surfaces in the absence of food.?


  Hungry so seek food, but also responding to temperature instead of food

  They move towards the temperature they are used to associating this with food

  Then they stay in this temperature
• In each experiment, the biologist exposed the surfaces to light that was dim and even, so he could see where the worms went. Apart from seeing where the worms went, suggest two reasons why the light needed to be dim and even?


  Dim worms live in dark so ensures a normal environment and doesn't impact normal behaviour

  Dim light ensures heat from light is not a variable -> also heat from lamp could kill worms
• In the test plot of land, identify the push stimulus and the pull stimulus?

  Push - legume

  Pull - grass
• When measuring the mean percentage damage to maize plants, 60 plants from each test plot were selected at random and examined. Describe how the maize plants could be selected at random?

  Make a grid of plot

  Use a number generator

  To generate coordinates
• In the test plot, bare ground was left between the maize and the grass species. Suggest an explanation why.?

  Reduce competition between maize and grass

  For light, nutrients, water
• The legume plants have nodules containing nitrogen-fixing bacteria on their roots. Explain how nitrogen-fixing bacteria could increase the growth of the maize. (2)?


  Nitrogen-fixing bacteria convert nitrogen in the air into ammonium compounds (in soil) which are converted into nitrates

  Maize uses nitrates for amino acid/ proteins or ATP
• A year after this investigation, the government of one country decided that their farmers should use these push-pull stimuli. How do these data support this decision? (3)

  1. Reduced % damage to maize plants / increased maize grain yield;
  2. Calculation to justify mp 1;
  3. standard deviation shows no overlap but need stats to show the significance of this difference;
  4. More profit / net income / greater income than additional cost (with push-pull);
  5. $322 extra / 408% more / $401 v $79 profit;