Plants

Question 1

Why do plants need water?

Answer 1

• Used in photosynthesis
• Carry dissolved minerals e.g. nitrates
• Keep cells turgid for support - without water pressure, the plant will wilt and droop
• Cooling the leaves - as water evaporates from the surface of the leaves, it removes heat energy from the plant

Question 2

Why do plants need minerals?

Answer 2

• Minerals are needed for the plant to carry out reactions
• They are used to make new substances in the plant e.g. chlorophyll
• Nitrate ions are needed to make proteins for growth

Question 3

What are the functions of roots?

Answer 3

• Absorbing minerals or ions
• Anchor or support the plant in soil

Question 4

How are root cells adapted to absorbing water?

Answer 4

• Root hair cells provide a large surface area so that water travels and mineral ions can be absorbed quicker
• The root hairs have thin cell walls, so the water travels over a shorter distance (faster rate of absorption of water)
• Don’t have chloroplasts because they don’t have light to photosynthesise

Question 5

How are mineral ions absorbed in root cells?

Answer 5

• The concentration of mineral ions in the root cell is higher than in the soil, because minerals move in the root by active transport - particles move against the concentration gradient, so root hair cells contain lots of mitochondria to release enough energy for this process to happen.

Question 6

What is the phloem?

Answer 6

• The phloem is a vascular bundle and is adapted to translocation, which is the movement of sucrose up and down the plant

Question 7

What is the xylem?

Answer 7

• The xylem is a vascular bundle adapted for transpiration, the movement of water and minerals up the plant due to loss of water in the plant

Question 8

How is the xylem adapted to its function?

Answer 8

• Xylem tissue is made up of dead cells joined together to form long hollow tubes so water flow is not slowed down.
• Xylem is lined lignin, which is waterproof and gives great strength and support
• Tiny pores allow water to enter and leave the xylem vessel

Question 9

How is the phloem adapted to its function?

Answer 9

• Sieve plates are perforated through which sucrose flow through
• Sieve tubes are attached to companion cells, which provide energy for the transport of substances

Question 10

What is the symbol equation for photosynthesis?

Answer 10

6CO^2+6H^2O —>C^6H^12O^6+6O^2

Question 11

How does temperature affect the rate of transpiration?

Answer 11

As temperature increases, the rate of transpiration increases, because as it gets warmer, particles have more kinetic energy so they will move faster. Water vapour molecules can then diffuse faster out of leaves and are lost more quickly.

Question 12

How does light intensity affect transpiration?

Answer 12

As light intensity increases, the rate of transpiration increases, because the plant will make photosynthesis faster, so the stomata will open to allow more carbon dioxide in, but more water vapour will diffuse out

Question 13

How does air flow affect transpiration?

Answer 13

As air movement increases, the rate of transpiration increases, because the water vapour molecules in the air are blown away, decreasing the concentration gradient between the air and the leaves

Question 14

How does humidity affect transpiration?

Answer 14

As humidity increases, the rate of transpiration decreases, because there is more vapour in the air, decreasing the concentration gradient between the air and the leaves, reducing the rate of diffusion of water molecules.

Question 15

What are the stoma?

Answer 15

Small hole for gas exchange, CO2 enters, O2 leaves. Its size of the opening is controlled by 2 guard cells.

Question 16

How do the guard cells control the stoma?

Answer 16

• When water moves into the guard cells, they become turgid and open the stomata
• When water leaves the guard cells, they became flaccid and close the stomata

Question 17

Describe the change in the size of the stomata

Answer 17

During daylight, the stomata opens because CO2 is required for photosynthesis, but water vapour can diffuse out too

Question 18

Why does the stomata change shape during the day?

Answer 18

• At midday, the temperature may be too high, making guard cells lose water, which close the stomata
• At night, the stomata closes as photosynthesis is not happening

Question 19

Describe transpiration

Answer 19

• Water is lost at the leaves through the stomata
• As water diffuses out, more water is pulled up through the stem
• All water molecules move as a column because water molecules are cohesive

Question 20

How to calculate the rate of transpiration

Answer 20

rate of transpiration=distance/time