Transport, Storage and Gas Exchange in Flowering Plants

Miss Rochford

Sixth Year Biology

In this topic:

• Uptake and transport of:

– Water and minerals

– Carbon dioxide

• Gas exchange

• Transport of photosynthesis products

• Modified food storage organs

Why do plants need a transport system?

• For photosynthesis and other metabolic processes, plants need:

– Water

– Carbon Dioxide

– Oxygen

– Minerals

– Nutrients

• These need to be transported within the plant

UPTAKE AND TRANSPORT OF

MATERIALS IN PLANTS

Root hairs and absorption

• Root hairs have many adaptations for absorption

Thin walls

Not covered by a cuticle

Large surface area by being numerous

Osmosis

Root hairs and absorption

• Soil water:

Less concentrated than root hair cells

• Water moves by osmosis into the root hair cells

• Cytoplasm in root hair:

Lots of dissolved materials

Movement of Water into Xylem

• How does this happen? DIFFUSION

Water moves from: To: Method

Root hairs Ground tissue Diffusion

Ground tissue Xylem Diffusion

Movement of Water into Xylem

Upward Movement of Water

• Two mechanisms involved:

1. Root Pressure

2. Transpiration

Root Pressure

• Build-up of water in roots causes a rise in pressure

• This pressure pushes water up through the xylem

• BUT, it’s not strong enough on its own.

• It works together with transpiration

Root Pressure: Guttation

Transpiration

• Helps to keep water moving upwards through the plant

• Water exits through stomata

Transpiration: the loss of water vapour from the aerial parts of a plant

Stomata: openings on the underside of leaves

Transverse Section of a Leaf (Learn labels)

Control of transpiration

Control Explanation

Waxy cuticle on leaves Prevents excess water loss

Stomata positioned underneath leaves

Lower rate of evaporation here

Stomata can open and close

This can reduce water loss when needed

Mineral uptake and transport

• Plants need minerals such as:

– Calcium

– Magnesium

– Nitrates

– Phosphates

– Sodium

– Potassium

Mineral uptake and transport

Diffusion

• Some minerals absorbed this way • Does not require energy • Also known as passive transport

Active Transport

• Some minerals are absorbed by active transport

• This requires energy

Uptake and transport of CO2

1. Atmospheric Carbon Dioxide

• Enters through stomata • Diffuses into photosynthesising cells in ground tissue

2. Carbon Dioxide from Respiration

• Respiration in the mitochondria of the leaf produces CO2

• This is also used for photosynthesis

Fate of products of photosynthesis

Oxygen

• Diffuses into air spaces in the leaf • Some used in respiration • The rest is diffused out of stomata

Fate of products of photosynthesis

Glucose

• Three possibilities: 1. Used immediately for Respiration 2. Stored as starch 3. Converted to sucrose and transported through

phloem as phloem sap

COHESION-TENSION THEORY

Amazing water transport in trees

Cohesion-Tension Model

• Water has high cohesion

Cohesion: the sticking of similar molecules to each other

Adhesion: occurs when different molecules stick together

• Water adheres to the walls of xylem

• Water’s cohesive force is greater than its adhesion to xylem

Cohesion-Tension Model

1. Transpiration involves water leaving through stomata

– Each water molecule pulls the next due to their high cohesion

2. This pulling of the water means that the water in xylem is under tension

3. Water can be pulled up to 150 m

Day

Night

Cohesion-Tension Model

FOOD STORAGE IN PLANTS

Food storage organs in plants

• Formed from Tap Roots

• Modified roots are swollen with food stores

• Examples:

– Carrot

– Parsnip

– Turnips

Modified Root

Food storage organs in plants

• Stems swell to form a food store

• Potatoes are underground stems, swollen with starch

• Another example = asparagus

Modified Stem

Modified Leaves

Food storage organs in plants

• Bulbs: a reduced stem and modified leaves

• Leaves are swollen and fleshy to store food

• Central apical bud is within the leaves

• Bulb is protected by dry scaly leaves

Modified Leaves

GAS EXCHANGE

Gas exchange in the leaf

• CO2 is needed for photosynthesis

• It diffuses into leaves through stomata

• It diffuses to the ground tissue through air spaces between cells

• Air spaces increase surface area of the leaf

Carbon Dioxide

Gas exchange in the leaf

• Oxygen diffuses from the ground tissue into the air spaces

• It exits through stomata

Oxygen

• Water vapour diffuses out through the stomata

• The process is known as TRANSPIRATION

Water vapour

Gas Exchange in Stems

Lenticels: small pores on a stem that function in gas exchange

Stomatal opening and closing (HL)

• Generally:

Time Stomata Reason

Day Open Gas exchange for photosynthesis

Night Closed Help reduce loss of water when gas exchange is not necessary

Stomatal opening and closing (HL)

• Environmental conditions can also cause stomata to close

Condition Behaviour of stomata

Windy weather

• Wind increases transpiration rate • Stomata close to minimise water loss

Calm conditions

Stomata open

High temp Stomata close to preserve water

Stomatal opening and closing (HL)

• Guard cells control stomatal opening and closing by controlling their turgidity

Turgid guard cells

• Swollen with water • Curve away from each

other • Stoma are open

Flaccid guard cells

• They have lost water • Cells are close together • Stoma are closed

Chapter 25: Transport, Storage and Gas Exchange

in Flowering Plants

DONE!!