Eutrophication, Leaf Structure and Transport in Plants

Seite 1

most respiration is carried out in the palisade cells

they are near the upper surface so they can absorb more light

if the stoma is open it is daytime and water is entering and leaving the cell

Structure

Function

Waxy Cuticle

This layer decreases water loss - is transparent so light can pass through

Upper Epidermis

Supports the leaf when the cells are turgid- Covered by waxy cuticle

Spongy Mesophyll Layer - Loosely-packed cells covered with a thin film of water allows diffusion of gases- Large air spaces

Vascular Bundle

Composed of xylem and phloem- provide transport and support

Lower epidermis

This layer has guard cells which control the opening and closing of stomata

Xylem - Cell walls thickened with lignin- Conducts water and mineral salts and gives mechanical support

Phloem

Transports sugars made during photosynthesis- Sieve plates separate adjacent cells

Palisade mesophyll

Cells are tightly-packed and contain many chloroplasts for maximum light absorption

Water and carbon dioxide need to from the soil intro the roots then to all parts of the plant (especially the leaves)

- transported in xylem vessels

- xylem vessels lose their cytoplasm and form long columns with walls thickened (and waterproofed) by lignin

Glucose is produced in the leaves and needs to be transported to non-photosynthetic parts

- transported by phloem

- columns but are living cells

W

Water travels by osmosis

Xylem is inside the veins and runs throughout the leaf

2. Water leaves the xylem and moves (by osmosis) from cell to cell

3. Some of it moves to cells for turgor or to be used in photosynthesis

4. 90% of water leaves via the stomata

5. Water evaporates in the air spaces of the spongy mesophyll and exits as a gas

Organic compounds are transported in the phloem = translocation

Sugar = Sucrose

Sucrose is moved from where it is produced or stored to where it will be utilized or stored

= moving sucrose from a source to a sink

Amino acids are also translocated to where they are needed

Use = making proteins

Treatment

Effect on rate

Explanation

No treatment

normal

normal

transpiration rate

Increased temperature

increased

Fast transpiration rate

In the dark

decreased

Slow transpiration rate

Increased humidity

decreased

Slow transpiration rate

Increased wind speed

increased

Fast transpiration rate

Removal of ½ of the leaves

decreased

½ times slower

Water is absorbed through the root hair cells

- low water potential in root hair cells compared with surrounding soil = osmosis

How does water move up the plant?

1. Root pressure: water enters root hairs by osmosis

2. Adhesion: Water molecules are attracted to the cellulose in the xylem vessels and move up them by capillary action

3. Transpiration pull: As water molecules evaporate off the spongy mesophyll and diffuse out of the stomata they 'pull' the water molecule behind them upwards

- downwards along a chain of water molecules in the cell = cohesion = sticking together and is caused by hydrogen bonds between water molecules

Leaf Structure 1. Upper Epidermis

No photosynthesis occurs because there are no chloroplasts

There is no transport of water and glucose

No gas exchange

2. Palisade Mesophyll

Photosynthesis occurs because there are lots of chloroplasts

No transport of water and glucose

No gas exchange

3. Spongy mesophyll

Photosynthesis occurs because there are chloroplasts

No transport of water and glucose

Gas exchange occurs

4. Lower Epidermis

No photosynthesis occurs

No transport of water and glucose

Gas exchange occurs

5. Xylem & Phloem

No photosynthesis occurs

There is transport of water and glucose

No gas exchange

6. Stomata

No photosynthesis

No transport of water and glucose

Only gas exchange occurs

7. Guard Cell

Only photosynthesis occurs

Eutrophication is the process by which a body of water becomes enriched in dissolved nutrients.

Excessive nutrients from fertilizers eg: nitrates and phosphateswashes from farmlands into rivers and streams.

This causes too much algae to grow.

The algae blocks sunlight from reaching aquatic plants below.

Aquatic plants die because they cannot photosynthesise.

Bacteria decompose the plants using up oxygen in the water - the B.O.D. (=Biological Oxygen Demand) of the water increases.

Aquatic animals die eg: fish due to lack of oxygen

Bacteria decompose these dead organisms using up even moreoxygen - the B.O.D. of the river rises even higher.

Ecosystem of the river is destroyed.

Water from the soil enters the plant through root hair cells. It then moves across the root cortex cells and into the xylem tubes. Water is then ‘pulled up’, the xylem vessels in the root and stem to replace the water that is lost at the leaves. The flow of water through the plant is called the transpiration stream. Mineral salts dissolved in the water also travel in this stream.

Xylem and phloem vessels together make the vascular bundle.

Xylem is made of dead, waterproof tubes. Lignin makes them waterproof. It’s specialised tissue in plants that transport waste and inorganic ions.

Xylem vessels contain no living material like cytoplasm. It helps their transport role because ir allows more water and minerals to be transported from the roots to the leaves.

Phloem is specialised tissue that transports the products of photosynthesis, mainly sucrose solution

Eutrophication

Leaf Structure

Plant Transport

Transpiration

Translocation