1. In an experiment, a leafy shoot was set up in a potometer and kept in a dark room for 2 hours. The set up was then transferred to a well-lit room for 2 hours.
a) What was the aim of this experiment? (1mk)
To investigate the effect of light on the rate of transpiration.
b) Explain the results which would be expected in each of the two experiments conditions. (3mks)
More water was lost in the light than in the dark. Rate of transpiration was greater in light than in the dark. This is because the stomata are fully open in light but less open or closed in the dark. In light, photosynthesis takes place hence no water used.
2. Explain how drooping of leaves on a hot sunny day is advantageous to plant. (2mks)
The leaves exposed a smaller surface area to the sun thus reducing transpiration. Excessive water loss.
3. Explain how environmental factors affect the rate of transpiration in flowering plants. (20mks)
- Temperature- high temperature increase transpiration. Low temperature lower transpiration.
Light intensity-more light increase transpiration, dim light lower transpiration.
Wind – strong wind increase transpiration, calm weather lower transpiration.
Humidity – High humidity lower transpiration, low humidity increase transpiration.
Atmospheric pressure- High atmospheric pressure increase transpiration.
Water availability-more water increase transpiration due to opening of stomata while little water lowers transpiration.
4. The diagram below represents a transverse section of a young stem.
a) Name the parts labeled A and B (2mks)
A - Epidermis
B – Pith
b) State the functions of the parts labeled C, D and E (3 marks)
C - Transport manufactured food/translocation
D - Produce new cells/divide giving new cells
E - Transport mineral salts and water.
c) List three differences between the section shown above and one
that would be obtained from the root of the same plant (3mks)
-Xylem in centre/star shaped.
-Phloem in arm of xylem
-No pith in root
-Roots hairs present in root
5. The diagram below represents the pathway of water from soil into the plant.
a) Name the structures labeled K and L (2 marks)
K - Root hair
L - Xylem vessel
b) Explain how water from the soil reaches the structure labeled L. (5mks)
Water moves from the soil into the root hair by osmosis. Because concentration of cell sap is higher than water in the soil; the cell sap of the root hair is diluted thus making it less concentrated than neighbouring cells; therefore water moves into the neighbouring cell. It is then actively secreted into L.
c) Name the process by which mineral salts enter into the plant. (1mk)
6. State two ways in which xylem are adapted to their function. (2mks)
Lignified/thickened to prevent collapsing.
Narrow to facilitate capillarity
No cross wall for continuous flow of water.
Side walls pitted to allow lateral movement of water and mineral salts.
7. What makes young herbaceous plant remain upright? (2mks)
Presence of xylem vessels
Presence of collenchymas
8. The diagram below represents part of phloem tissue
a) Name the structures labeled R and S and a cell labeled T.
R- sieve pore/plate
T- Companion cell
b) State the function of the structure labeled S. (1mk)
c) Explain why xylem is a mechanical tissue (2mks)
9. Name the
a) Material that strengthens xylem tissue. (1mk)
b) Tissue that is removed when the bark of a dicotyledonous plant is ringed. (1mk)
10. How are xylem vessels adapted for support? (1mk)
They are strengthened by lignin hence supporting the stem.
11. What is the role of vascular bundles in plant nutrition? (3mks)
- Xylem - Transports water and mineral salts to photosynthesizing cells
– Phloem - Transports manufactured foods from the leaves creating high concentration gradient.
- Veins - Supports the leaf to be upright for maximum absorption of light for photosynthesis
12. a) Name two tissues which are thickened with lignin. (2mks)
b) How is support attained in herbaceous plant? (1mk)
-Turgidity of parenchyma cells
-Presence of collenchyma cells
13. The diagram below represents a transverse section through a plant organ.
a) From which plant organ was the section obtained? (1mk)
b) Give two reasons for your answer in (a) above. (2mks)
i) Presence of root hairs
ii) Phloem between rays of xylem (star shaped xylem).
c) Name the parts labeled J, K and L (3mks)
J - Epidermis
K - Phloem
L - Xylem
d) State two functions of the part labeled M. (2mks)
Absorbs water and mineral salts from soil.
14. Describe how water moves from the soil to the leaves in a tree. (20mks)
- Adhesion- force of attraction between unlike molecules
- Due to the force of adhesion water tends to stick to the walls of vessels containing it.
- Cohesion- forces of attraction between like molecules - Cohesion between water molecules prevents the water column from breaking.
- Root pressure- due to pressure generated by the root’s endodermis
- Capillary due to narrowness of xylem.
- Transpiration pull- as water evaporates from the leaf’s surface more is absorbed
- After the water reaches the leaves cells, it passes the cells by osmosis from the xylem. Water vapour diffuses out through stomata.
15. State two ways in which the root hairs are adapted to their function.
- Absence of cuticle to allow diffusion of water.
- Thin walled to reduce distance of diffusion.
- Elongated to increase surface area for absorption of water and mineral salts.
- Presence of large vacuole to increase concentration gradient between cell sap and soil water
16. The diagram below represents a plant tissue.
(a)Name the tissue
(b)Name the cells labeled K and L
(C)What is the function of the companion cell?
Supply nutrients and energy to the sieve tubes
17. In an experiment to determine the effect of ringing on the concentration of sugar in phloem, a ring of bark from the stem of a tree was cut and removed. The amount of sugar in grammes per 16cm3 piece of bark above the ring was measured over a 24 hour period. Sugar was also measure in the bark of a similar stem of a tree which was not ringed. The results are shown in the table below
a) Using the same axes, plot a graph of the amount of sugar against time (6mks)
b) At what time was the amount of sugar highest in the;
i) Ringed stem (1mk)
ii) Normal stem (1mk)
c) How much sugar would be in the rigged stem if it was measured at 03 45 hours. (2mks)
0.79 ± 0.02 grammes
d) Give reasons why there was sugar in the stems of both trees at 06 45 hours. (2mks)
The food that had been manufactured the previous day had been converted to soluble sugars and was being translocated to other parts of the plant.
e) Account for the shape of the graph for the tree with ringed stem between:
i) 06 45 hours and 15 45 hours (3mks)
- There was low concentration of sugar early in the morning as there was little translocation.
- As day progresses the light intensity increases and more food is manufactured thus more translocation increasing concentration of sugars.
ii) 15 45 hours and 00 45 hours (2mks)
- The light intensity is decreasing reducing rate of photosynthesis. Less food is manufactured, hence less is translocated.
- As it turns dark there is no photosynthesis reducing concentration of sugar translocated.
f) Other than sugars name two compounds that are translocated in phloem. (2mks)
- Amino acids
- Soluble fats/lipids.
18. Explain why plants shed off their leaves. (2mks)
i) Reduce transpiration
ii) Eliminate excretory wastes on the leaf
19. a) What is the importance of transpiration to plants?
- Cool the plant
- Remove excess water
- Enhance absorption and distribution of water and mineral salts
b) Give adaptive features which enable a plant to reduce the loss of
- Few and small leaves
- Reduced leaf size
- Sunken stomata
- Thick cuticle.