transport systems (plants)

Question 1

Why do organisms need transport systems

Answer 1

Multicellular organisms have multiple cells layers and diffusion to all cells would be too slow to meet all the organisms needs
This is why multicellular organisms need transport systems
Smaller SA : VOL ratio

Question 2

Why do unicellular organisms not need transport systems

Answer 2

Diffusion, osmosis and active transport through the cell membrane are sufficient to meet the unicellular organism’s needs
Small diffusion distances
Substances move around cell easily without transport systems
Large SA : VOL ratio

Question 3

Transpiration meaning

Answer 3

The evaporation of water from the parts of the plant that are above ground (leaves, stem, flowers)

Question 4

How does transpiration occur?

Answer 4

Occurs through the evaporation of water at the surfaces of the spongy mesophyll cells followed by the diffusion of water vapour through the stomata

Question 5

List the functions of transpiration

Answer 5

Transporting mineral ions
Providing water to keep cells turgid in order to support the structure of the plant
Providing water to leaf cells for photosynthesis
Keeping the leaves cool as heat energy is removed from the leaves when water evaporates

Question 6

Factors affecting the rate of transpiration

Answer 6

Air movement, light intensity, humidity and temperature

Question 7

7. Light intensity effect on transpiration

Answer 7

As light intensity increases the transpiration rate increases
Increased light intensity increases the rate of photosynthesis as more stomata tend to be open in bright light to maximise photosynthesis
So the stomata open to allow gas exchange
When this happens, water vapour diffuses out of the stomata

Question 8

Temperature effect on transpiration

Answer 8

As temperature increases, the transpiration rate increases
When temperatures are high, water vapour molecules have more kinetic energy and move around faster
So they are more likely to move out of the stomata by diffusion
Water molecules diffuse out of the leaf quicker

Question 9

Air movement effect on transpiration

Answer 9

As wind speed increases, the transpiration rate increases
When it is windy, water molecules that diffuse out of the stomata are quickly blown away from the leaf
This increases/maintains a concentration gradient and more water vapour diffuses out of the leaf

Question 10

Humidity effect on transpiration

Answer 10

As the humidity increases, the transpiration rate decreases
Humid air contains a high concentration of water vapour, reducing the diffusion gradient between the inside of the leaf and the outside air
So less water vapour diffuses out of the leaf

Question 11

What do the xylem and phloem make up in a vascular plant?

Answer 11

The transport system

Question 12

Role of phloem in plant

Answer 12

Transports sucrose, plant hormones and amino acids from where they are produced to where they are needed

Question 13

Phloem structure

Answer 13

Made up of several types of living cells
End walls have pores (sieve plates)
Companion cells load and unload solutes to and from the phloem
Bi-directional movement in phloem - glucose is needed everywhere
Provides energy for active transport
Transport of solutes – sucrose, amino acids, plant hormones; relies on active transport (which needs energy from respiration)

Question 14

Role of xylem in plant

Answer 14

Transports water, hormones and mineral ions from the roots to other parts of the plant

Question 15

16. Xylem structure and function

Answer 15

Made up of types of dead cells
Hollow continuous tubes with no end walls
Lignin strengthens the cell walls and provides support
Uni-directional movement of substances in xylem
Transport in the xylem relies on the transpiration stream (pull)
Strengthens and supports plant
Substances move through xylem passively (no energy required)

Question 16

Root hair cells

Answer 16

Single-celled extensions of epidermis cells in the root
They grow between soil particles and absorb water and minerals from the soil

Question 17

Root hair cells adaptations

Answer 17

Adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport)
They contain mitochondria which release energy for active transport
Root hairs increase the surface area of plant roots, increasing the rate at which water and minerals can be taken up

Question 18

Process that root hair cells take up water and mineral ions from the soil by

Answer 18

Root hair cells take up mineral ions from the soil by active transport
The water concentration of the cell cytoplasm is reduced due to the presence of mineral ions
Water moves into the root hair cell by osmosis

Question 19

21. Describe the route of water through the plant

Answer 19

Water moves by osmosis, into the root hair cells, through the root cortex and into the xylem vessels
Once the water gets into the xylem, it is carried up to the leaves where it enters the mesophyll cells
Pathway is:
Root hair cell  root cortex cells  xylem  leaf mesophyll cells

Question 20

What apparatus can we use to investigate the rate of transpiration

Answer 20

A potometer

Question 21

2 types of potometer

Answer 21

Mass potometer:
Measures the change in mass of a plant as a measure of the amount of water that has evaporated from the leaves and stem
Bubble potometer:
Measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation consequently pulling up water through the stem to replace it
The bubble moves through the tube, showing the rate of transpiration

Question 22

Apparatus that can be used during the practical to simulate different factors that affect the rate of transpiration

Answer 22

Light intensity – lamp
Airflow – set up fan or hairdryer
Temperature – control temperature of room
Humidity – spray water in a plastic bag and wrap around the plant

Question 23

Results of practical: investigate the role of environmental factors (light intensity) in determining the rate of transpiration from a leafy shoot

Answer 23

As light intensity increases, the rate of transpiration increases
This is shown by the bubble moving a greater distance in the time when the lamp was placed closer to the leaf

Question 24

List the limitations and solutions for these limitations of the experiment (light intensity from a leafy shoot using a potometer)

Answer 24

The potometer equipment has a leak:
Solution – ensure that all equipment fits together rightly around the rubber bungs and assemble underwater to produce a good seal and minimise the entry of oxygen
The plant cutting has a blockage:
Solution – cut the stem underwater and assemble equipment underwater to minimise opportunities for air bubbles to enter the xylem and affect the results of the experiment
The potometer has shown no change during the experiment:
Solution – use the plant cuttings as soon as they have been cut as transpiration rates may slow when cuttings are no longer fresh

Question 25

How does water travel through a plant?

Answer 25

1. The root hair cells have a large surface area to volume ratio. Water is absorbed by osmosis. 2. Water moves through the root hair cells by osmosis along a water potential gradient 3. Water molecules enter the xylem. They are pulled up by the ‘transpiration pull’ created by the movement of water through the cells in the leaves. 4. The cohesive forces of attraction between water molecules maintains the continuous column of water in the xylem 5. The water molecules evaporate from the cells into airspaces in the leaf. This reduces the water potential of the cells 6. This causes water molecules to move from the xylem into the leaf cells by osmosis 7. The evaporated water molecules diffuse out through the stomata

Question 26

What is the purpose of companion cells?

Answer 26

They help with the life processes of the phloem cells e.g., respiring to produce energy for the phloem to move organic molecules

Question 27

Are phloem cells alive?

Answer 27

Yes, they need to be alive to help transport

Question 28

Are xylem cells alive?

Answer 28

No, so that there is no obstruction to the flow of water by cytoplasm or organelles

Question 29

What is the purpose of lignin?

Answer 29

Lines xylem walls, thickens stem Waterproof and very strong Stops cells collapsing inwards and gives the stem support

Question 30

What is the movement of sucrose and amino acids around the plant known as?

Answer 30

Translocation

Question 31

What sugars does the phloem transport?

Answer 31

Sucrose – it is soluble in water yet more energy efficient than glucose or fructose

Question 32

What is the purpose of sieve plates?

Answer 32

They allow cells to have cell walls yet also allow contents to travel between cells

Question 33

What happens when plants cannot transpire?

Answer 33

Water loss is prevented in the plant Other gases can still diffuse into and out of the leaf Photosynthesis can still occur and produce glucose The plant will not wilt or become flaccid The plant may overheat as the heat energy the water particles carry before they evaporate is trapped Less absorption of mineral ions through the roots

Question 34

How could you use hydrogen carbonate indicator to investigate the effect of light intensity on net gas exchange in a leaf?

Answer 34

Put the leaves in test tubes containing the same volume of hydrogen carbonate indicator with bungs Make sure the test tubes allow different levels of light into them eg by use of aluminium foil, gauze wrap Leave the leaves for a few hours Observe the colour changes Purple - leaf had access to light and could photosynthesise leading to a net release of oxygen in the test tube Yellow - leaf had no access to light and could only respire leading to a net release of carbon dioxide in the test tube Orange red - control tube Tube that allowed partial light through to the leaf. The rate of respiration is equal to the rate of photosynthesis leading to no net gas exchange in either direction of either gas

Question 35

What is a biotic factor?

Answer 35

A living factor or something to do with a living factor eg: species of a plant