Transpiration and Translocation

Question 1

Translocation

Answer 1

The movement of dissolved glucose (produced in photosynthesis) from the leaves to the rest of the plant by the phloem tubes.

Question 2

Purpose of Translocation

Answer 2

Transport sugar to cells in the plant so that it can be used for respiration, growth or glucose storage (starch).

Question 3

What do phloem tubes transport?

Answer 3

CELL SAP: glucose dissolved in water - sugar made in the leaves can be transported long distances and across multiple cells.

Question 4

Bidirectional

Answer 4

The phloem can transport substances in either direction, so, up or down the plant.

Question 5

Phloem Vessels’ Specialisation

Answer 5

In between the adjacent cells in the tube, there is a semi-permeable membrane with pores, that allows (cell sap) to move through.

Question 6

Transpiration

Answer 6

Evaporation of water from the leaves’ stomata: this pulls water up from the roots through the xylem and is called transpiration.

Question 7

Transpiration Stream

Answer 7

The constant movement of water up the plant through the xylem due to transpiration.

Question 8

Xylem tubes are…

Answer 8

long and hollow tubes found in the vascular bundles alongside the phloem which transport water and mineral ions in the plant.

Question 9

Xylem Vessels Specialisation

Answer 9

Made up of dead xylem cells which are joined together with no end walls between them. In the xylem tubes, transport only goes one way.

Question 10

Xylem vessels have thick walls strengthened by…

Answer 10

LIGNIN

Question 11

The process of transpiration provides:

Answer 11

Water to cells which keeps them turgid.
Water to cells (in the leaf) for photosynthesis.
Mineral ions to leaves: e.g. nitrates for amino acids which form proteins/ magnesium for chlorophyll production.

Question 12

Factors Affecting Rate of Transpiration: Temperature

Answer 12

Higher temperatures increase the rate of transpiration because water evaporates faster in higher temperatures.

Question 13

Factors Affecting Rate of Transpiration: Humidity

Answer 13

Lower humidity increases the rate of transpiration because the drier the air, the steeper the concentration gradient of water molecules between the air and leaf,

Question 14

Factors Affecting Rate of Transpiration: Wind Speed

Answer 14

More wind increases the rate of transpiration because the wind removes the water vapour quickly maintaining a steeper concentration gradient.

Question 15

Factors Affecting Rate of Transpiration: Light Intensity

Answer 15

Higher light intensity increases the rate of transpiration because stomata open wider to let more carbon dioxide into the lead for photosynthesis.

Question 16

Root Hair Cells take in water through…

Answer 16

OSMOSIS

Question 17

Root Hair Cells take in mineral ions through…

Answer 17

ACTIVE TRANSPORT - contain lots of mitochondria to transfer energy to do this.

Question 18

How are root hair cells adapted to their function?

Answer 18

1. the hair like extension of the cell maximises its surface area greatly, which is a significant advantage, given that the root hair cell is an exchange surface, where the diffusion of minerals from the soil and water through osmosis happens. The greater the surface area, the more active transport can happen, the more minerals and water the plant has to survive.
2. the root hair cell has a thin cell membrane, so that the diffusion of minerals like magnesium and nitrate ions through active transport is easier, as well as water, decreasing diffusion time and distance. This makes osmosis more efficient and quick.
3. the root hair cell is packed with mitochondria, which are the site of respiration. the cell requires a lot of respiration to occur, so that more energy is released to be used in active transport.
4. the root hair cell has a large vacuole, which stores water with dissolved solutes, maintains a low water potential inside the cell, increasing osmosis into the cell, maximising the amount of water the plant gets to be used in photosynthesis, and keeping cells turgid.

Question 19

Describe the pathway of water through a plant and explain the factors that affect the rate of transpiration.

Answer 19

1. water diffuses into root hair cells in the roots of the plant, from the soil, via. osmosis:
   root hair cells have long hair like projections which maximise their surface area in order to make available a greater exchange surface for more water to diffuse into the cell via. osmosis. they have a large vacuole which contains water with dissolved solutes, decreasing the water potential in the cell, so more water molecules diffuse into the cell from a high water potential to a low water potential. the root hair cell also has a thin cell wall, making diffusion distance and time smaller, and the osmosis more efficient.
2. the xylem tubes in the vascular bundles, are responsible for carrying out transpiration. they are long hollow tubes, strengthened by lignin to withstand the high water pressures, and carry out capillary action.
3. up the stem, through the vascular bundles, the water is delivered to the leaf, where it diffuses through the spongy mesophyll tissue and eventually diffuses out of the stomata.

Factors that affect the rate:
1. light intensity - the greater the light intensity, the more open the stomata are so that more CO2 can get in and more photosynthesis can occur, when there is an abundance of light. as the stomata stay open for longer, the more water has an opportunity to diffuse out. as more water is removed from the plant, more has to be absorbed into the transpiration stream to make up for the loss.

2. as temperature increases, more water evaporates from the stomata, resulting in water loss so the transpiration rate increases.
3. humidity - if the air is drier, there is a steeper concentration gradient between the plant and the air, so more water diffuses into the air, more is lost and the rate of transpiration increases.
4. wind speed - if wind speeds are particularly high, water is removed from stomata due to the force of the wind.

Question 20

Explain how the structure of guard cells allows them to control the opening and closing of stomata.

Answer 20

1. guard cells are sensitive to environmental stimulus - they can open and close the stomata accordingly to the light intensity, temperature and humidity of the air.
2. they have a bean shape, allowing them to be flexible and bend. this means that when the guard cells are turgid indicating a high concentration of water in the plant, they bend away from each other, opening the stomata, and allowing for water to evaporate from the plant, since it is in good supply. however, when the plant needs to conserve its water supply, they naturally become flaccid and the stomata close, preventing water loss through evaporation and diffusion.
3. they have a thicker cell wall on the outside and a thinner cell wall in the inside, When the guard cells take up water and become turgid, the thicker inner walls make the cells bulge outward. The thinner outer walls allow the guard cells to stretch and pull apart, opening the stomata. Conversely, when the guard cells lose water, the turgor pressure drops, and they close the stomata.

Question 21

In translocation, the movement of sugars is driven by….

Answer 21

a difference in pressure between the source, where the sugars are loaded into the phloem so the leaf, and the sink, where they are delivered