UWCSEA - IGCSE Biology - Plant Transport Answers 1

What is path (naming each part in order) from water in the soil to the leaf?

water around roots-->root hair cells--> xylem in roots --> xylem in stem --> xylem in leaves --> spongy mesophyll cells and palisade cells

What is the effect of 1. temperature 2. light intensity 3. humidity on the rate of transpiration?

1. Temperature increases transpiration as water molecules have more energy and so evaporate more quickly, diffusion as water vapour out of the leaf 2. Light intensity increases transpiration, as stomata open for gas exchange to allow carbon dioxide into the leaf for photosynthesis, so more water can leave the leaf 3. Humidity decreases transpiration; as if it is more humid there is more water vapour in the air; therefore there is a less of a concentration gradient; so diffusion of water vapour is slower;

How does red dye and celery show the movement of water in a plant?

Dye is taken up the xylem; travels up the length of the plant; cutting the stem shows dye is inside;

Where would you find xylem and phloem? How could you identify which was which from a picture of the roots, stems and leaves of plant?

In vascular bundles; xylem are larger tubules, phloem are smaller;

How is the structure of root hair cells related to their function?

Long and thin; creates large surface area; for absorption of water; and mineral ions; like nitrates and phosphates;

How would the the number of air spaces in a plant affect the rate of transpiration?

More air spaces leads to faster rate of transpiration; as there is more air surround spongy mesophyll cells; leading to more evaporation;

How would the number of stomata affect the rate of transpiration?

More stomata = faster rate of transpiration; as there are more routes or water to leave the leaf;

What are nitrates and magnesium used for in plants? What happens if plants don't get enough of these from the soil?

Nitrates for making proteins (amino acids); not enough causes stunted growth and poorly formed roots; magnesium used for chlorophyll synthesis; not enough and leaves turn pale/white due to no chlorophyll;

What is the definition of transpiration?

The evaporation of water from the surfaces of the spongy mesophyll; through the stomata; out of the leaf; causing water to move through xylem from roots to leaves;

What is translocation? Give an example and say what is moving from where to where and why.

The movement of sugars; such as sucrose; from the source; e.g. leaf; to the sink; e.g. roots; for storage; also can flow from storage organs, like potato; back to the stem and growing areas of the plant when required;

How does transpiration occur? Detailed explanation here.

Water molecule evaporate into the air spaces; from cells of the spongy mesophyll; then move down their concentration gradient; out of the stomata; this causes water to be pulled up the xylem; as water is cohesive so sticks together; this causes a tension 'pull', pulling more water up from the roots where it was absorbed;

What are the functions of xylem and phloem?

Xylem transports water; and mineral ions; such as nitrates and phosphates; magnesium and sodium; from the roots to the leaves; Phloem transports sugars; such as sucrose; from the place they are being produced- the leaf; to where they are being stored in the roots, or in the fruits/flowers;