TRANSPORT OF MATERIAL IN PLANT BIOLOGY QUESTIONS AND ANSWERS

TRANSPORTATION OF MATERIALS IN PLANT

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1. Define transport

Is the movement of substances from one pan of the body to another.

2. Explain the necessity of transport in plants and animals

The importance of transport in plant and animal are as follows;

• make nutrients move from one point to another.
• movement of respiratory gases i.e. oxygen and carbon IV oxide.
• elimination of metabolic wastes.
• movement of hormones.
• movement of water.
• movement of salts.
• movement of enzymes.

3. i) Describe the structure and function of root hair

• root hairs are found near the root tip.
• They are cells with elongated finger-like projections which are in contact with soil particles.
• They are permeable to water and mineral salts hence are used to absorb Water and mineral salts.
• Their large number offers a large surface area for absorption of water and mineral salts.

ii) State ways in which the root hairs are adapted to their functions

• The root hair is long/narrow/numerous to increase surface area for absorption of water and mineral salts.
• many mitochondria in cytoplasm to supply energy for active transport of mineral salts.
• are thin walled to speed up the rate of absorption of Water and mineral salts.

4. Give the similarities and differences between a monocotyledonous and dicotyledonous stem

Similarities

• Both are used for protection.
• both conduct water, salts and food.
• both have epidermis, cortex, pericycle and vascular bundles.

Differences

Monocotyledonous

• vascular bundles are many and scattered.
• some have hollow pith or pith is absent.
• no cambium layer therefore cannot.
• undergo secondary growth very.
• little cortex.

Dicotyledonous

• vascular bundles are few and arranged in a concentric ring near the epidermis.
• pith large and well developed.

5. State the differences between the internal structure of a root and a stem.

• no cambium layer therefore cannot.
• undergo secondary growth.
• very little cortex.
• presence of cambium therefore.
• undergoes secondary growth.
• The cortex has several layers of cells.

6. Name the transport structures of a flowering plant

• xylem vessels and tracheids transport water and mineral salts from the soil.
• Phloem vessels translocate manufactured food from leaves to other parts of the body.

7. State the ways in which xylem vessels are adapted to their function

• lignified/thickened to prevent collapsing.
• narrow to facilitate capillary.
• no cross walls for continuous flow/column of water.
• have bordered pits for lateral movement of water.

8. Why do flowering plants need water?

Plants needs water for

• photosynthesis.
• transport.
• Turgidity helps in plant support.
• solvent i.e. medium for chemical reactions.
• cooling effect during transpiration.
• seed germination.

9. Describe the movement of water from the soil to the leaves of a tall plant

• Soil water exists as a thin film in the soil, between soil particles.
• the concentration of cell sap of root hair is greater than that of the surrounding solution in the soil, thus drawing the Water molecules across the cell wall and cell membrane into the root hair by osmosis.
• water drawn into the root hair cell dilutes the cell sap making it less concentrated than that in the adjacent cortex cells of the root.
• due to osmotic gradient water moves from the root hair cells into the cortex by osmosis, from cell to cell by osmosis, across the endodermis by active transport into xylem vessels of the root that conduct water into xylem vessels of the stem into xylem vessels of the leaves.

Stem

• Once in the stem water moves up the plant aided by the narrowness of the xylem vessels (capillary), root pressure, attraction of water molecules to each other (cohesion).
• Attraction of water molecules to the Walls (adhesion) from the stem water enters the xylem of leaves.
• water moves in the xylem vessels of the stem in a continuous (uninterrupted) water column up to the tree leaves.

Leaves

• once in the leaves water moves into the mesophyll cells by osmosis as water evaporates from the spongy mesophyll cells their sap becomes more concentrated than the adjacent cells as the result water flows into the cell from other surrounding cells which in turn takes in water from xylem vessels within the leaf veins this creates a pull(suction force) called transpiration pull that pulls a stream of water from xylem vessels in the stem and roots .
• The transpiration pull maintains a continuous column of water from the roots to the leaves.

10. Name the process by which mineral salts enter into a plant

• active transport.
• diffusion.

11. Explain the forces that make water and mineral salts move through a plant

• mineral salts are taken up due to diffusion because of the concentration gradient between the mineral ions in sap and those in soil solution.
• Active transport involves energy in the form of ATP due to respiration which forces mineral salts through a plant against a concentration gradient.
• water moves by osmosis through a semipermeable membrane of root hairs and between cells of the stem.
• in stem water moves by cohesion(attraction of water molecules to each other)
• it also moves by adhesion(attraction of water molecules to walls)
• capillarity is due to narrowness of xylem vessels.
• transpiration pull occurs When Water vapour evaporates from substomatal chambers into the air
• root pressure is a force that pushes Water up the stem from the roots and causes guttation /exudation.

12. Explain the uptake of mineral salts by plants

• plants require mineral salts for metabolism and proper functioning of their bodies
• mineral salts are taken up from the soil into the root hairs in form of solution by active
• transport which requires energy
• active transport involves substances called carriers taken up together with water and are then carried to the stems and leaves
• the main process involved in uptake and movement of mineral salts is active transport

13. i) What is transpiration?

Is the loss of water from plant in form of water vapour to the atmosphere

ii) Name the sites through which transpiration takes place in a plant

• stomata (stomatal transpiration)
• lenticels (lenticular transpiration)
• cuticle(cuticular transpiration)

iii) State the importance of transpiration to plants

• cooling the plant
• transport of water
• transport of mineral salts
• excretion of excess Water from plants
• excess transpiration causes wilting

14. Explain the structural factors that affect the rate of transpiration in plants

• number of stomata i.e. the more the stomata the higher the rate and vice versa
• turgidity of the guard cells which control the opening and closing of stomata when they are open transpiration rate is high
• size of leaves where the larger the surface area the higher the rate of transpiration
• leaf fall leads to lower rate of transpiration and also drying of leaves reduces rate of transpiration
• Thin cuticle reduces distance through which water evaporates hence increases transpiration rate. Absence of cuticle also increase rate of transpiration

15. Explain the environmental factors that affect rate of transpiration in plants

• high temperature increases the rate of transpiration and low temperature reduces the rate.
• humidity when high increases rate and when low reduces the rate.
• transpiration rate is higher in moving air (wind) than in still air.
• high light intensity increases internal temperature hence higher rate of evaporation leading to higher rate of transpiration.
• availability of water in the soil leads to more absorption hence more loss to the atmosphere.
• atmospheric pressure when high leads to more evaporation and when low leads to low rate evaporation of water.

16. State the structural differences between xylem vessels and sieve tubes

• sieve tubes have cross wall while xylem vessels have none
• xylem vessels are lignified while sieve tubes are not
• Sieve tubes have cytoplasm elements while xylem vessels have none.

17. State the adaptations of plants which enable them to reduce water loss

• thick waxy cuticle
• reduced leaf size/thorns/spines
• shedding of leaves
• Sunken stomata. Water vapour accumulates in the depression of stomata lowering the water vapour concentration gradient leading to lower rate of evaporation
• rolling of leaves

18. State the factors that cause increase in the rate of transpiration from leaves

• increased light intensity.
• low relative humidity.
• temperature.

19. Explain how drooping of leaves on a hot sunny day is advantageous to a plant

reduces surface area exposed to sun therefore reducing cuticular transpiration

20. Explain how aquatic and terrestrial plants are adapted to deal with problems of transpiration

a. Mesophytes

• they grow in soils with enough water
• water loss is perfectly balanced by absorption of more from the soil
• no special adaptations

b. Xerophytes

• They grow in dry conditions.
• The roots grow very deep to absorb water.
• succulent/fleshy leaves to store water.
• a few stomata which are sunken.
• thickened waxy cuticle.
• The leaves are hairy and often folding.
• Some leaves are needle-like/spines or scales.
• leaf surfaces are reduced i.e. small leaves.
• All these adaptations are to reduce water loss.

c. Hydrophytes

• plants that grow in water
• presence of sclereids
• leaves are broad
• leaves have many stomata on upper side only (none on the lower surface)
• some leaves float on water
• absence or reduced leaf cuticle
• large air spaces
• some leaves are submerged
• poorly developed or reduced vascular bundles

21. What is translocation

Is the movement of manufactured food substances to the parts where they are required

22. Name the tissue which is responsible for translocation of manufactured food in flowering plants

phloem tissue

23. Name the processes that bring about the translocation of manufactured food

• active transport
• Diffusion
• Mass flow
• Cytoplasmic streaming

24. name the compounds that are trans-located in phloem

• sugars
• amino acids
• hormones e.g auxin
• oils/lipids
• resins
• vitamins

25. Describe an experiment you would carry out in order to demonstrate that phloem transports manufactured food substances in a plant

i) Ringing experiment

• cut a ring in the bark including the phloem from the stem of a woody plant.
• phloem is found next to or just beneath the bark.
• observe daily for some time(more than three weeks).
• a swelling of the bark appears above the ring.
• This is due to accumulation of food from leaves.
• The bark of a second similar plant is removed carefully leaving the phloem intact.
• swelling does not appear.

ii) Use the radio-active tracers

• The plant is exposed to carbon containing radio-active carbon C14.
• C14 is found in the end products of photosynthesis.
• It is finally detected in phloem.
• C14 is found to move in both directions.

iii) Collecting exudate from stylets of aphids

• aphids feed on certain plant phloem using their stylets.
• Aphid mouth parts are dissected using a sharp razor.
• exudes from the mouth parts are collected and then analysed.
• sucrose is found to be a major component of the exudates.
• This proves that phloem trans-locates manufactured food substances.

26. Describe an experiment you would carry out to demonstrate that xylem transports water

i. Either

• cut a stem of a young plant or twig of a tree under water
• or else uproot a young herbaceous plant and wash the soil gently
• put some water in a beaker and add a dye i.e. eosin or red ink and place the cut stem or young plant in a beaker
• leave for time e. g. between 20 minutes and one hour
• cut a thin section of stem or leaf.
• mount it on a slide and examine it under a microscope.
• observe and note the distribution of the dye or ink.
• The dye appears only in the xylem vessels.

ii. OR

• use radio-active tracers, C14 in form of carbon
• ring a plant then put it in a container containing radio-active phosphorus solution
• The radio-active phosphorus is later detected in the leaves.