Chapter 8: Transport in plants

Question 1

why do plants have branching shapes?

Answer 1

due to it giving them a larger surface area in relation to their volume. It means that most of their cells are close to the surface.

Question 2

xylem

Answer 2

a plant tissue made up of dead empty cells joined end to end; it transports water and mineral ions and helps support the plant.
They don’t contain any cytoplasm or nuclei, their walls are made of cellulose and lignin. Lignin is very strong and helps keep the plants upright. (mechanical support).

Question 3

phloem

Answer 3

a plant tissue made up of living cells joined end to end; it transports substances made by the plant such as sucrose and amino acids. Contains cytoplasm but no nuclei.
Activity controlled by th companion cells.

Question 4

Pits

Answer 4

They have small holes on their sides called pits where water can enter and move from one vessel to another.

Question 5

Sieve plates

Answer 5

Walls that have partially broken down to form sieve plates in phloem tubes.

Question 6

adaptations of xylem: the cells are dead with no contents

Answer 6

water can flow easily through a tube

Question 6

lignin

Answer 6

a hard string waterproof substance that forms the walls of the xylem vessels.
In leaves, the xylem vessels in the vascular bundle help the leaf to be held flat to provide a large surface area to absorb sunlight.

Question 7

adaptations of xylem: there are no cross walls between the dead cells

Answer 7

there is a continuous tube for water to flow through all the way from the roots to the leaves.

Question 8

adaptations of xylem: the walls of the vessels contain lignin

Answer 8

lignin is solid and makes sure the vessels are open and do not collapse allowing the water to flow through easily.

Question 9

adaptations of xylem: the diameter of the vessels is between about 15 micrometres and 200 micrometres

Answer 9

this is narrow enough to make sure the column of water inside them does not break: but wide enough to allow a lot of water to flow through.

Question 10

RHC

Answer 10

at the very tip is a protective cap to protect the root it grows through the soil. The rest of the roots are covered by a layer of cells called the epidermis. The root hairs are formed from some of the cells in the epidermis.
each root hair is a long epidermal cell. Root hairs do not live for a very long. As the root grows they get damaged by the soil particles and are replaced by new ones.

Question 11

the function of the RHC

Answer 11

Is to absorbs water and minerals in the form of the soil. We have seen that water moves into a root hai by osmosis.

Question 12

the pathway of water through to the plant

Answer 12

As cytoplasm and cell sap inside the r0oot hair are quite concentrated solutions. The water in the soil is normally a more dilute solution. Water therefore diffuses into the root hair down its concentration gradient through the partially permeable cell surface membrane. The long thin root hairs have a large surface area which increases the uptake of water and minerals ions.

Question 13

the pathway of water through to the plant (2)

Answer 13

-water is drawn up the xylem to replace water in the leaf due to water loss. This creates a respiration stream.
-water enters the root hair cell through osmosis down concentration gradient as the soil water has water potential to the root hair cell sap.
-water crosses the living cells of the cortex through-
osmosis through the cells
pulled by transportation through freely permeable membrane cell walls (in between cells).
-Near the center of the root a layer of cells with a waxy cell wall that prevents water, from moving through the cell wall forcing all water to go through the living cells to enter the xylem vessels.
-This allows the cell membrane to control substances that enter the xylem.

Question 14

transpiration

Answer 14

-water in the mesophyll cell from a thin layer of moisture on their surfaces(this helps with diffusion of CO2 in the cells).
-The water evaporates from the large surface areas of the spongy mesophyll cells into airspace, this creates a high concentration of water molecules in air spaces inside and low outside.
-water vapour diffuses down the concentration gradient of one of the leaves into the surrounding air through the opened stomata.
-Water cannot diffuse into the leaf due to the air spaces being too saturated with water vapour. This must be absorbed from the soil and drawn up the plant.

Question 15

transpiration pull

Answer 15

a force produced by the loss of water vapour leaf which reduces the pressure at the top of xylem vessels.

Question 16

transpiration pull: how does it work?

Answer 16

the pressure on the top of the xylem vessels is less than the pressure at the bottom in the roots due to the loss of water vapour by transpiration.

Question 17

cohesion

Answer 17

Water in the xylem can flow upwards like this because water molecules have a strong tendency to stick to each other. there is a force of attraction between them. and so when one water molecule moves upwards others stick with it and move up as well. The water therefore stays together as one continuous column and does not break apart.

Question 18

potometer

Answer 18

means water measurer.

Question 19

reservoir

Answer 19

prevent air bubbles from entering the plant and move the bubbles along the capillary tube.

Question 20

capillary tube

Answer 20

to be kept horizontal to avoid bubbles moving.

Question 21

air bubbles

Answer 21

inserted by removal of the tube from water.

Question 22

temperature

Answer 22

higher the temperature teh greater the kinetic energy of water molecules.
water evaporates faster from the surface of mesophyll cells and water vapour diffuses out of the leaf into the air more quickly.

Question 23

wind

Answer 23

air that contains a lot of water vapour moves away quickly.
This means that there is always a diffusion gradient for the water vapour because there is loss outside the leaf than in the air spaces inside the leaf.

Question 24

humidity

Answer 24

higher the humidity less water vapour will diffuse out from the leaves. because there is not much diffusion gradient for the water between the air spaces inside the leaf and the wet air outside.

Question 25

increased factors

Answer 25

transpiration will happen very quickly. the plant may lose water from its leaves faster than it can take it up from its roots. the individual cells in the plant lose so much water that they become flaccid. The tissues in the leaves are no longer supported by the turgid cells pushing outwards against one another. The leaves become floppy and this is called wilting.

Question 26

wilting(of a plant)

Answer 26

losing more water than it can take up so the cells lose their turgidity.

Question 27

translocation

Answer 27

the movement of sucrose and amino acids in phloem from sources to sinks.

Question 28

source

Answer 28

part of a plant that releases sucrose or amino acids to be transported to other parts.

Question 29

sink

Answer 29

part of a plant to which sucrose or amino acids are being transported and where they are used pr stored.

Question 30

source to sink (summer/ spring)

Answer 30

leaves are the main source of sucrose and amino acids due constant production of sucrose. The sinks are the roots and flower (or any other part of the part). Roots change the sucrose to starch to store, flowers change the sucrose to fructose for nectar and later, sucrose may be used to produce sweet-tasting fruits to attract animals.

Question 31

Autumn winter or hot summers

Answer 31

during this time plants do not photosynthesis. they survive by the stores of starch in the root which are converted into sucrose and transported into other parts of the plant.

Question 32

phloem and xylem difference

Answer 32

phoem ca transfer sucrose in either direction- up and down the plant. this isn’t true for the transport of water in the xylem vessels. that can go upwards because transpiration alwys happens at the leaf surface and this provides the pull to draw up water up the plant.