(2.51-2.58) Diffusion/System + Flowering Plants

Why can simple unicellular organisms rely on diffusion for movement of substances? (3)

Substances can diffuse directly in and out of the cell

low SA:V ratio

quick rate of diffusion

Why do multicellular organisms need a transport system?

Small surface area to volume means they need transport systems to ensure the cells all get what they need.

What is the role of the phloem?

To transport sucrose and amino acids between the leaves and other par of the plant.

What is the role of the xylem?

To transport water and mineral ions from the roots to other parts of the plant.

Features of a xylem (4)

Lignified

Dead cells

Hollow tube

Upwards stream

Features of a phloem (2)

Up and downwards stream

Perforated end walls

How do root hair cells absorb water from the soil?

Through osmosis.

How do root hair cells absorb mineral ions from the soil?

Through active transport via ATP

How are root hair cells adapted for absorption? (3)

Elongated- Large SA- more area for absorption

Thin walls- shorter diffusion distance

Concentrated cell sap- water will always enter cell due to steep conc. grad.

What is transpiration?

The evaporation and diffusion of water from the surface of a plant.

What is transpiration pull?

The drawing up of a continuous stream of water up through the xylem.

What is meant by cohesion in relation to transpiration?

Attractive force between the water molecules which keeps it as a steady stream.

What is meant by adhesion in relation to transpiration?

Attraction between water molecules and the walls of the xylem

What are the main functions of the transpiration stream? (4)

Transport of mineral ions

Keeping cells and plant turgid

Keep plant cool

Photosynthesis

What are the factors affecting the rate of transpiration?

Light intensity

Temperature

Air Movement

Humidity

How does light intensity affect transpiration?

low light intensity

= closed stomata

= water vapour cannot diffuse into atmosphere

= lower rate of transpiration

How does temperature affect transpiration?

High temp

= high kinetic energy

= higher evaporation

= higher rate of diffusion through the stomata

How does air movement affect transpiration?

higher air movement

= removal of water vapour around leaf surface

= air is less humid/ less saturated

= steeper conc. grad

= higher rate of transpiration

How does humidity affect transpiration?

high humidity

= increases water molecules outside the leaf

= decreases conc. gradient

= lower rate of transpiration

What can be used to investigate the role of environmental factors in determining rate of transpiration?

Use a potometer to measure the movement of an air bubble and estimate the rate of water intake by a plant.

What is the formula for measuring the water uptake?

πr² * distance moved by air bubble

Precautions- write down why:

Plant needs to be healthy

Stem needs to be cut at an angle

Stem needs to be cut 2-3cm up

needs to transpire

to maximise surface area

ensure the xylem is exposed

Precautions- one reason why:

Stem needs to be cut underwater

Potometer needs to be set up underwater

Plant needs to be inserted underwater

Potometer needs to be airtight

no air bubbles

Precautions- write down why:

Potometer needs to be watertight

Leaves need to be dry

Allow acclimatisation time

Keep other variables constant throughout

Prevent leakage (skewed results)

Allow a conc. gradient

Allow stream to start acting in a new environment

To ensure a variable other than the one being measures is not impacting results