Plant Growth and Development
11 Grade 10 General Science questions on Plant Growth and Development, with worked marking schemes. 11 questions are available on this topic in full.
Question 1
5 marksA potted seedling was placed next to a classroom window. After a few days its shoot had bent towards the window.
(a) Explain how auxins brought about the bending of the shoot. (3 marks)
(b) State two ways, other than fruit ripening, in which plant hormones are used in farming. (2 marks)
(5 marks)
Marking scheme
(a) 1 mark each (3 marks): - Auxins are made at the shoot tip and move down the shoot. - Light from one side makes the auxins move to, and build up on, the shaded side of the shoot. - The higher auxin concentration makes cells on the shaded side lengthen faster than cells on the lit side, so the shoot bends towards the light. (b) Any two of the following, 1 mark each (2 marks): - Rooting powder (auxin) helps cuttings, such as tea or roses, form roots. - Synthetic auxins (such as 2,4-D) are used as selective weedkillers in maize and wheat farms. - Gibberellins are used to break seed dormancy or to increase fruit size (for example, in grapes). - Auxins or gibberellins are used to produce seedless (parthenocarpic) fruits. - Cytokinins are used in tissue culture to raise many plantlets, for example banana plantlets. - Some hormones are used to make crops such as pineapples flower at the same time.
Question 2
5 marks(a) State three differences between primary growth and secondary growth in plants. (3 marks)
(b) Explain two ways in which secondary growth is important to a tall tree such as a eucalyptus. (2 marks)
(5 marks)
Marking scheme
(a) Any three of the following, 1 mark each (3 marks). Both sides of a difference are needed for the mark: - Primary growth comes from apical meristems at the tips of shoots and roots; secondary growth comes from lateral meristems (vascular cambium and cork cambium). - Primary growth increases length or height; secondary growth increases thickness or girth. - Primary growth happens in all plants; secondary growth happens mainly in dicotyledonous woody plants (perennials). - Primary growth produces primary tissues; secondary growth produces secondary xylem (wood), secondary phloem and bark. - Primary growth takes place in the young regions near the tips; secondary growth takes place in the older regions of the stem and root. (b) Any two of the following, 1 mark each (2 marks): - The wood (secondary xylem) gives strength and support, so the tall stem can carry a large crown without breaking. - More xylem carries more water and mineral salts to the many leaves. - More phloem carries more food from the leaves to the other parts of the tree. - The cork (bark) protects the stem from injury, water loss and infection.
Question 3
4 marksApart from a seed coat that water cannot pass through, outline four causes of seed dormancy in plants. (4 marks)
(4 marks)
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1 markThe increase in the thickness of the trunk of a jacaranda tree over the years is mainly the result of cell division in the
A. vascular cambium
B. phloem sieve tubes
C. xylem vessels
D. apical meristem
(1 mark)
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3 marksExplain how annual rings form in the stem of a grevillea tree growing in an area that has one wet season and one dry season each year. (3 marks)
(3 marks)
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1 markFruit traders in Nairobi ripen green bananas quickly by keeping them in a closed room together with ripe fruits. Which plant hormone is responsible for this ripening?
A. abscisic acid
B. cytokinin
C. ethylene
D. gibberellic acid
(1 mark)
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1 markSeeds of some acacia trees fail to germinate because they have a hard seed coat that water cannot pass through. Which treatment is most suitable for breaking this dormancy?
A. planting the seeds deep in compacted soil
B. scratching the seed coat with sandpaper
C. storing the seeds in a dry, cool place
D. keeping the seeds in an airtight container
(1 mark)
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1 markWhich of the following is an example of development rather than growth in a plant?
A. an increase in the number of cells at a shoot tip
B. an increase in the size of the vacuoles in new cells
C. the formation of flowers on a mango tree
D. the enlargement of young cells behind a root tip
(1 mark)
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1 markWhich of the following seeds undergoes hypogeal germination?
A. castor oil plant
B. pumpkin
C. maize
D. bean
(1 mark)
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Create a free account to see itQuestion 10
4 marksA learner planted bean seeds and wanted to measure the growth of the seedlings over three weeks.
(a) State two measurements, other than mass, that she could take to show the growth of the seedlings. (2 marks)
(b) Explain why dry mass is a more reliable measure of growth than fresh mass. (2 marks)
(4 marks)
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4 marksExplain how each of the following affects the growth and development of a maize plant:
(a) light (2 marks)
(b) water (2 marks)
(4 marks)
Marking scheme
(a) Light, any two of the following, 1 mark each (2 marks): - Light is needed for photosynthesis, which makes the food used for growth. - With too little light, the plant becomes etiolated: tall, thin, weak and yellow, with small leaves. - Light is needed to make chlorophyll, so leaves turn green. - The length of daylight (photoperiod) affects when some plants flower. - Light coming from one side makes the shoot grow towards it (phototropism). (b) Water, any two of the following, 1 mark each (2 marks): - Water is a raw material for photosynthesis. - Water keeps cells turgid, which is needed for cells to enlarge and for leaves and young stems to stay firm. - Water is the medium in which enzyme reactions take place. - Water carries dissolved mineral salts from the soil to the growing parts. - Lack of water leads to wilting and stunted growth, and can reduce the number and size of cobs and grains.
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