Author: Philip Colls
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Plant hormones booklet revision questions           NAME:
Q1. 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.
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(b)     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.
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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.
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 (2)
(d)     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.
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(2)
(ii)     In this investigation, the physiologists investigated the leaves of pear trees.
Explain why the results might be different for other species.
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(1)
(Total 8 marks)

Q2. Scientists investigated the response of lateral roots to gravity. Lateral roots grow from the side of main roots. The diagrams show four stages, A to D, in the growth of a lateral root and typical cells from the tip of the lateral root in each stage. All of the cells are drawn with the bottom of the cell towards the bottom of the page.
 
(a)     Describe three changes in the root tip cells between stages A and D.
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2. _________________________________________________________________
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3. _________________________________________________________________
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(3)
(b)     The scientists’ hypothesis was that there was a relationship between the starch grains in the root tip cells and the bending and direction of growth of lateral roots.
Does the information in the diagram support this hypothesis? Give reasons for your answer.
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(c)     The diagram shows the distribution of indoleacetic acid (IAA) in the lateral root at Stage B.
 
Explain how this distribution of IAA causes the root to bend.
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____________________________________________________(2) (Total 8 marks)
Q3. (a)     Give one similarity and one difference between a taxis and a tropism.
Similarity ___________________________________________________________
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Difference __________________________________________________________
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(2)
Scientists investigated tropisms in the roots of tomato plants. They grew tomato plants from seeds on vertical agar plates, as shown in Figure 1. The top of each plate was made of agar gel containing no salt. The bottom of each plate was made of one of the following:
•        agar gel containing no salt
•        agar gel containing salt.
Typical results for growth of the roots are shown in Figure 1.
Figure 1
 
(b)     What do these results show about the responses of the roots of tomato plants to gravity and salt?
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(c)     In root tips of tomatoes, IAA is transported out of the cells by a carrier protein. In roots of tomatoes, high concentrations of IAA inhibit cell elongation.
The scientists’ hypothesis was that salt causes a change in the number of IAA carrier proteins in cells in different parts of the root tip.
Figure 2 shows two cells, L and R, in the root tip of a tomato plant.
Figure 2
 
Explain why this root tip would grow away from salt.
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___________________________________________________ (3)  (Total 8 marks)
Q4. A large number of roots from many genetically identical bean plants were cut into short pieces. The pieces were sorted into groups, depending upon their distance from the root tip. Some pieces from each group were used to find the mean dry mass of their cells. Thin sections cut from other pieces were examined with a light microscope to find the proportion of dividing cells and the mean volume of the cells. The graph shows the results. The diagrams below the graph show the appearance of cells in light microscope sections at different distances from the root tip.
 
(a)     Suggest two variables, other than genotype, which need to be controlled to ensure similar root growth in different plants. In each case give the reason for your answer.
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2. _________________________________________________________________
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(2)
(b)     Suggest how the proportion of dividing cells in a thin section could be determined.
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(c)     Explain the change in the proportion of dividing cells with increasing distance from the root tip.
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(d)     Using the graph and diagrams, suggest how a root tip gets longer.
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(3)
(Total 9 marks)

Mark schemes
Q1.
(a)     Diffusion;
Ignore references to simple / facilitated 
Accept active transport 
1
(b)     1.      Causes plant to bend / grow towards light / positive phototropism; 
2.      (Light) required for photosynthesis; 
2
(c)     1.      More kinetic energy / faster movement of molecules;
2.      More diffusion; 
Ignore references to opening stomata.
Answer should be in context of more but comparative statement only necessary once. 
2
(d)     (i)      1.      Thick cuticle on upper surface / thin cuticle on lower surface / few stomata on upper surface / no stomata on upper surface; 
2.      More diffusion / shorter diffusion pathway (on lower surface); 
1. Ignore cuticle only on upper surface. Ignore references to more or less waxy. 
2. If candidate writes about stomata accept ref to greater area for diffusion. 
2
(ii)     Different species have different (qualified) properties;
Eg cuticle thickness 
Leaf size 
Number of stomata 
1
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Q2.
(a)     Three changes described;;;
Neutral nucleus shrinks, since it doesn’t
Eg
1.      Formation / growth of vacuole;
2.      Formation of starch grains / amyloplasts;
2. Accept starch grains get bigger
3.      Movement of grains / amyloplasts towards bottom of cell;
Note − list rule applies
4.      Cells get longer / wider / larger;
3 max
(b)     1.      Grows sideways before starch grains form;
Q
2.      Bending starts when / as grains form;
3.      More bending as grains increase in number;
3. Ignore starch grain growth references
4.      More elongation (of cells) / growth (of roots) downwards as starch grains increase / move;
5.      Bending starts before grains move down;
6.      Could be related to vacuole;
6. Ignore references to nucleus
3 max
(c)     1.      (IAA) at bottom of root / where IAA concentration high inhibits expansion / elongation (of cells);
2 and 3 need reference to expansion / elongation, not just growth
2.      (IAA) at top of root / where IAA concentration low leads to expansion / elongation (of cells);
2. Accept less inhibition
2
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Q3.
(a)     1.      Similarity − directional response (to a stimulus) / movement
         towards / away from a stimulus;
2.      Difference − taxis (whole) organism moves and tropism a growth (response).
Must be clear which one, taxis or tropism, they are referring to
Taxis occurs in animals / motile organisms and tropism occurs in plants
2
(b)     1.      Grow in direction of / towards (pull of) gravity;
Accept: tropism for growth
Ignore: pulled by gravity
Accept: positively geotropic / gravitropic
2.      Grow away from salt;
Accept: negatively chemotropic / halotropic
1 and 2. Ignore: references to bends / moves
3.      Salt has more effect (than gravity).
Accept: converse statement for gravity
Note: all three points may appear in one sentence
3
(c)     1.      More carriers in (cell) L / lower in R;
Accept: left for L and right for R / side nearer salt for L
2.      (So) less IAA in (cell) L / more IAA in (cell) R;
Accept: more IAA moves out of L / less IAA moves out of R
3.      (So) more (elongation) growth in L / less (elongation) growth in R.
Accept: less inhibition of growth in L / more inhibition of growth in R;
3
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Q4.
(a)     two environmental or developmental variables and explanation;
examples,
all plants of the same age, so same time for cell divisions / differentiation;
all plants given the same watering, so same amount of water for
cell expansion;
(reject reference to photosynthesis)
all plants given same light, so same rate of photosynthetic;
same temperature, so enzymes / named metabolic process at
optimum temperature;
same named ion / minerals in soil(e.g. nitrate),
so same available for a named function,
(e.g. amino acid / protein synthesis);
2 max
(b)     count cells using microscope;
count number of cells in cell division / where chromosomes visible;
and then the total number of cells in field of view;
2 max
(c)     only cells at tip have ability to divide / cells further back don’t divide;
cells further back differentiating / named example of
(accept reference to loss of totipotent cells)
differentiated tissue / too old / reduction in plant hormone;
cell wall too thick / vacuole too large to allow division;
2 max
(d)     new cells added at tip;
cells increase in volume / larger;
increase in length (of cells);
as vacuole s get larger;
due to uptake of water (by osmosis);
3 max
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