Transport system in Plants

To function properly, organisms must exchange substances, like _____ ________ ____ _____, with their environment

food molecules and waste

Why don’t unicellular organisms like ameoba need speciallised exchange surfaces?

• Unicellular organisms, like amoebas, have large surface areas relative to their volume, meaning the distance from the surface of the cell to the centre is small

  • Consequently, they don't need specialised exchange surfaces or transport systems, as diffusion, osmosis, and active transport through the cell membrane are sufficient for their needs

Why do multicellular organisms need exchange surfaces?

Multicellular organisms, like humans, have bodies composed of many cells

These organisms have multiple cell layers, making the distance from the surface to the centre too long for diffusion alone

Diffusion to all cells would be too slow to meet the organism's needs, so larger organisms require transport systems

What is the role of the xylem?

Multicellular organisms, like humans, have bodies composed of many cells

These organisms have multiple cell layers, making the distance from the surface to the centre too long for diffusion alone

Diffusion to all cells would be too slow to meet the organism's needs, so larger organisms require transport systems

Which substance strenghtens and supports the thick walls of the xylem?

lignin

why is xylem is hollow tube?

the xylem is made up of dead cells which have lost there end walls and have no cytoplasm forming a continious hollow tube which allows water to flow more easily by reducing the resistance to the flow.

The transport in xylem is ___ way

one

The transport in xylem ____ ___ require energy

does not

The transport in xylem requires energy. TRUE OR FALSE

FALSE

In the xylem water is pulled up to the leaves due to ___________

transpiration

Why does water enters the roots?

The water enters the root by osmosis from a high to low water potential.

What is the role of the phloem?

The role of the phloem is to transport sucrose and amino acids from where they are produced or stored, to where they are needed

Explain the structure of the phloem

phloem are made up of sieve tube cells, they are living cells made of cellulose which have pores in the end walls (sieve plates) allowing dissolved sugar to move from cell to cell. They also have no nucleis and few organless to reduce the resistance to the flow of cell sap

In the phloem substance moves via ______ ______ which requires ______

active transport, energy

What are root hair cells?

• Root hair cells are tiny, single-celled extensions of epidermis cells in the root

How are root hair cells adapted for its functions?

• Root hair cells are adapted for the efficient uptake of water (by osmosis) and mineral ions (by active transport)

  • Root hairs increase the surface area of plant roots, increasing the rate at which water and minerals can be taken up

  • They contain mitochondria which release energy for active transport

What is the route of water throughtout the plant

root hair cell → root cortex cells → xylem → leaf mesophyll cells

define transpiration

The evaporation of water vapour from the surface of a plant

Why is transpiration useful for plants?

• Transpiration is useful for plants, having several functions:

  • Drawing water up to the leaves from the roots

  • Keeping the leaves cool as heat energy is lost from the leaves when water evaporates

  • Transporting mineral ions (eg. nitrates)

  • Preventing wilting by providing water to keep cells turgid

  • Providing water for photosynthesis

What are the enivronmental conditions that affects the rate of transpiration?

• There are several environmental conditions which have an impact on the rate of transpiration:

  • Air movement

  • Humidity

  • Temperature

  • Light intensity

How does air movement affect transpiration?

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

How does temperature affect traspiration?

As temperature increases, the transpiration rate increases As temperature increases, the kinetic energy of water molecules increases. Water molecules with increased kinetic energy move around faster and more likely to diffuse out of the stomata.

How does humidity affect transpiration?

As humidity increases, the transpiration rate decreases, When it is humid, there is an increase in water molecules outside of the leaf. This affects the diffusion concentration gradient. As a result, there is a decrease in the rate of diffusion of water vapour out of the leaf.

How does light intensity affect transpiration?

As light intensity increases, the transpiration rate increases. Light intensity affects stomatal opening - the higher the light intensity the greater the number of stomata that are open, which increases the diffusion of water vapour out of the leaf.

The loss of water vapour from the leaves of a plant is called _____.

transpiration

A piece of apparatus used to investigate factors affecting transpiration is called a _____.

potometer

There are two main types of potometer: a _____ potometer and a _____ potometer.

mass, bubble

A mass potometer measures a change in _____ of a plant.

mass

A bubble potometer measures the _____ of water by a stem.

uptake

Water uptake by the stem is used as a measure of the amount of water being lost through _____.

evaporation/transpiration

The movement of water into the stem occurs because water lost from the leaves creates a pull called the _____ pull.

transpiration

A bubble potometer commonly contains a _____ tube.

capillary

The capillary tube contains an _____ bubble that can be used to measure water uptake.

air

The distance moved by the air bubble is measured in _____. potometer

millimetres (mm)

Four environmental factors that can affect transpiration are temperature, humidity, light intensity and __________

wind movement/airflow

Increasing light intensity generally causes the rate of transpiration to _____.

increase

Increasing temperature generally causes the rate of transpiration to _____.

increase

Increasing humidity generally causes the rate of transpiration to _____.

decrease

Increasing wind movement generally causes the rate of transpiration to _____.

increase

In bright light, more _____ open.

stomata

Stomata open to allow _____ dioxide into the leaf for photosynthesis.

carbon

When more stomata are open, more _____ vapour can evaporate from the leaf.

water

The movement of air removes humid air from around the leaf and maintains a steeper _____ gradient.

concentration

High humidity means there is less of a water vapour _____ between the leaf and surrounding air.

concentration gradient

When setting up a bubble potometer, the shoot should be cut _____ water.

Under

When setting up a bubble potometer, why is the shoot cut underwater?

To prevent air entering the xylem.

When setting up a bubble potometer, what could happen if air enters the xylem?

It could form a blockage and prevent normal water movement.

When setting up a bubble potometer, the apparatus must be completely _____.

airtight

When setting up a bubble potometer, what can be used to seal gaps around the apparatus?

Petroleum jelly.

When setting up a bubble potometer, why must the apparatus be airtight?

to prevent leaks that could affect the movement of the air bubble and make the results inaccurate.

When setting up a bubble potometer, what should be done to the leaves before measurements begin?

The leaves should be dried.

When setting up a bubble potometer, why should the leaves be dried?

Water on the leaves could affect the results.

When setting up a bubble potometer, how is a single air bubble introduced into the capillary tube?

The capillary tube is removed from the beaker of water to allow a single air bubble to form, then placed back into the water.

When setting up a bubble potometer, what does the air bubble allow the student to measure?

The distance travelled by water as it is taken up by the plant.

When investigating the effect of light intensity on transpiration using a bubble potometer, what piece of equipment is used to change light intensity?

A lamp.

When investigating light intensity using a bubble potometer, how can light intensity be changed?

By changing the distance between the lamp and the plant.

Before measuring transpiration in the light-intensity investigation, how long should the plant be allowed to adapt?

In the light-intensity investigation using a potometer, what is recorded before starting the timer?

The starting position of the air bubble.

In the light-intensity investigation, how is the rate of transpiration calculated from the bubble movement?

Distance travelled by the bubble ÷ time.

In the light-intensity investigation, what is the time period used to calculate the rate of transpiration using a potometer?

30 minutes.

In the light-intensity investigation, what should be done to the bubble before repeating the experiment?

Reset the bubble using the reservoir.

What is the main limitation when investigating light intensity using a lamp?

Moving the lamp changes temperature as well as light intensity.

Why is temperature a confounding variable when investigating light intensity using a lamp?

A lamp closer to the plant produces higher light intensity but can also heat the plant, and temperature independently affects transpiration.

Why does the lamp make it difficult to investigate only the effect of light intensity using a potometer?

Changing the lamp distance changes both light intensity and temperature.

What apparatus problem could cause inaccurate results in a bubble potometer?

An imperfect seal causing a leak.

How can leaks be reduced when setting up a bubble potometer?

Ensure the equipment fits tightly around the rubber bungs and use petroleum jelly to seal gaps.

How could you investigate the effect of airflow on transpiration using a potometer?

Use a fan or hairdryer to change the airflow around the plant.

How could you investigate the effect of humidity on transpiration using a potometer?

Spray water into a plastic bag and wrap it around the plant to increase humidity.

How could you investigate the effect of temperature on transpiration?

Carry out the investigation in different temperatures, such as a cold room and a warm room.

Plant roots absorb water from soil.

This water is transported to the leaves and then moves into the air.

Identify which of these processes is used to absorb water from the soil.

A Active transport

B Diffusion

C Evaporation

D Osmosis

Osmosis

Name the tissue that transports water to the leaves.

xylem

Name the process that moves water vapour into the air.

transpiration

Identify which of these reduces the movement of water from the leaves into the air.

A High light intensity

B Low air humidity

C Low air temperature

D Windy conditions

low air temperature

Give two uses of water in a plant.

Support/turgor/maintaining the rigid structure of plant cells; [1 mark]

Photosynthesis; [1 mark]

Cooling: [1 mark]

Reactions/solvent/transport of mineral ions/named mineral ion; [1 mark]

Explain how the structure of a root hair cell is adapted to absorb water. (2 marks)

A root hair cell has a long, thin extension which increases its surface area. This large surface area allows the cell to absorb more water from the soil by osmosis.

Give one difference between osmosis and diffusion. (1 mark)

Osmosis is the movement of water molecules only, whereas diffusion can involve any type of molecules.

A student investigates the effect of light on the volume of water taken up and lost by a plant shoot in one hour.

The table shows the student's results.

(i) Explain these results.

(ii) Give two abiotic variables the student should control.

i) In light conditions, more water is taken up and more water is lost by the plant compared to dark conditions. This is because, in the light, the stomata are open, allowing more water vapour to evaporate from the leaves. The evaporation of water from the leaf surface creates a transpiration stream (or transpiration pull), which sets up a water potential gradient and draws more water up through the plant. Some of the water taken up is not lost but is used by the plant to fill cells, maintain turgor, support growth, and for photosynthesis.

ii) Temperature

Humidity

Another student uses this apparatus and a stop clock to find the mean (average) rate of water taken up by a plant shoot.

(i) Name the apparatus used by the student.

(ii) Describe how the student could use this apparatus to find the mean rate of water taken up by the plant.

i) potometer

ii) To find the mean rate of water taken up by the plant using this apparatus, the student should measure the distance that the air bubble moves along the capillary tube over a set period of time, such as 30 minutes. The student can calculate the volume of water taken up by multiplying the distance the bubble travels by the cross-sectional area of the tube, or by using the scale on the apparatus to read the volume directly. After each measurement, the reservoir should be used to reset the bubble to its starting position. The student should repeat the experiment several times and calculate the mean rate of water uptake from the results.