1. Give the term for the evaporation of water from leaves.
Answer
The evaporation of water from leaves is called transpiration.
2. Describe some functions of transpiration.
Answer
Transpiration supplies water to maintain cell turgidity, supports photosynthesis by delivering water to leaf cells, and facilitates the upward transport of mineral ions from the roots to the leaves.
3. Name the cells that control the size of the stomata.
Answer
The cells that control the size of the stomata are called guard cells.
4. Is the leaf a system ?
Answer
No, the leaf is an organ.
5. Describe how epidermis, palisade mesophyll and spongy mesophyll are adapted for their functions.
Answer
The epidermis covers and protects the plant. It is a transparent tissue that allows light to pass through easily.
The palisade mesophyll is the main site of photosynthesis. It consists of regularly shaped, tightly packed cells that contain numerous chloroplasts to maximize light absorption.
The spongy mesophyll is the main site of gas exchange. It consists of irregularly shaped cells with many air spaces between them, allowing gases to diffuse rapidly.
6. Name the three organs in the plant organ system that transports substances around a plant.
Answer
Roots, stem and leaves.
7. Water and mineral ions are absorbed from the soil by root hair cells. Explain why these cells contain large numbers of mitochondria.
Answer
Root hair cells take up mineral ions by active transport against the concentration gradient (from low concentration in the soil to higher concentration in the cells). Aerobic respiration in the mitochondria provides the energy required for active transport.
8. Explain some environmental factors that would increase the rate of transpiration.
Answer
High temperature: Increases the kinetic energy of water molecules, causing them to evaporate more quickly from the leaf surface.
High light intensity: Stimulates stomata to open wider in bright light, allowing more water vapor to diffuse out.
High air movement (wind): Removes water vapor from around the leaf surface, maintaining a low concentration of water vapor outside the stomata and creating a steep concentration gradient for rapid diffusion.
Low humidity: Results in drier air with less water vapor, which increases the concentration gradient between the inside and outside of the leaf, enhancing the rate of diffusion.
9. Give the reason why plants close their stomata.
Answer
To prevent water loss and wilting.
10. A student uses a microscope to look at the lower epidermis, and counts the number of stomata in one field of view. He uses this count to estimate the number of stomata in 1 mm2 of the leaf. Suggest how the student could improve his estimate.
Answer
He must count the number of stomata in more fields of view (a minimum of five) and then calculate the mean number of stomata.
11. There are more stomata on the lower surface than on the upper surface of a leaf. Suggest why this is an advantage for a plant.
Answer
Lower surface has lower temperature so less water lost by evaporation (or transpiration).