Principles of Organisation in plants

Function of a leaf

Photosynthesis occurs here

Function of a stem

Transport of substances

Function of Flowes

reproduction of bees

Function of root

Water and mineral ions uptake

How are leaves adapted for photosynthesisi

It has an upper epidermis, palisade mesophyll layer, spongy mesophyll, lower epidermis, guard cell, stomata, air space, xylem and phloem, epidermis cells and waxy cuticle.

How does a waxy cuticle protect the leaf

Waterproof- reduces water loss via transpiration, prevents pathogens from entering.

How does the upper epidermis protect the leaf

Covers the surface and protects the leaf, transparent layers to allow light to pass through for photosynthesis

How does the palisade mesophyll layer protect the leaf.

Contains many chloroplasts ( containing chlorophyll) to absorb sunlight

How does the spongy mesophyll protect the leaf.

spongy air pockets to allow gasses to diffuse through easily

How does the lower epidermis protect the leaf?

Covers the surface and protect the leaf, contains openings called stomata.

How does the guard cell protect the leaf.

Cells are used to open and close the stomata.

How does the stomata protect the leaf

allows carbon dioxide to enter and oxygen to leave the leaf for photosynthesis, usually closed in low light/ when dark

What subcellular structures are in a guard cell

Chloroplast, vacuole, cell wall, nucleus, stoma, inner cell wall.

What does a swollen guard cell mean?

The stoma is open so it is full of water ( turgid) . It is only open during the day to allow light, oxygen and carbon dioxide to pass through.

Why do guard cells swell

Guard cells swell allowing the stomata to open to allow gaseous exhcange. ( water sensitive)

What does a shrunken guard cell mean?

Guard cells shrink, loose water ( flaccid ) Guard cells shrink which closes the stomata to reduce gaseous exchange. ( light sensitive)

Why is it important to the plant that stomata can be opened and closed

It allows Carbon dioxide to eneter the plant for photosynthesis and the stomata can close to reduce water loss.

Structure, direction of flow, substances transported, process of the xylem

Strcuture: Continuous hollow tube ( no end walls between cells). Made of dead cells which thicken walls stiffened with lignin.

Direction of flow: roots to flowers only

substances transported: water and ( dissolved ) mineral ions

process: transpiration

Structure, direction of flow, substances transported, process of the phloem?

Structure : made with living Cells. Cells have end wall with perforations (because they are transporting larger substances)

Direction of flow: up and down

substances transported: amino acids & (dissolved) sugars

Process: Translocation

What is translocation?

The movement of dissolved sugars around the plant through the phloem tissue, sugards are made in the leavs so they need to be moved to other parts of the plant in the phloem for respiration, growth and storage.

Companion cells key geature is that is contains many mitochondria for energy used for active transport.

What is Transpiration

Evaporation and movement of water away from the plants leaves from insdie of the plant.

Water evaporates from the leaves ( mainly via stomata) this pulls water into the leaf from the stem or branches along the xylem vessels, this draws water up th3e stem or trunch of the plant or tree

more water is absorbed by osmosis at the roots as this water is drawn out ( down the concentration gradient)

Compare the xylem and the phloem

Xylem

• moves water one direction

• made with dead cells

• transporation process

• osmosis from the roots

• no end walls

• stiffened with lignin

• mineral ions and water

Phloem

• Translocation

• has end walls

• sieve plates - perferated cells

• transports amino acids and dissolved sugars

• companion cells

• uses active transport

Both

• Transport systems

• found in roots and steams, leaves

• part of the vascular bundle.

What is the transpiration stream?

Starts at the roots which have root hair cells to increase surfacr area. Here the water move into the roots through osmosis down the concentration gradient.

What environmental condition could speed up/ slow down transpiration

Temperature

humidity

light intensity

wind

How does light intensity affect the rate of transpiration

Correlation : As the light intensity increases the rate of transpiration also increases

Explanation: Higher light intensity means a faster rate of photosynthesis as the stomata stays open for longer so there are more gaseous exchange. This means the guard cells are open for longer and holding more water so more water is diffusing out of the plant.

How does temperature affect the rate of transpiration?

As the temperature increases the energy of the particles also increase

Explanation: The particles are gaining more energy so as they are heated up they are turning into a gas quicker so will evaporate faster.

How does wind affect the rate of transpiration?

The higher the wind the faster the rate of transpiration

Explanation Wind blows the water out so more water is put in.

There is a high concentration in the leaf and a low concentration

under the leaf. As the water diffuses the particles will reach the

equilibrium. when winds comes it removes the gas from under the

leaf so the process starts again.

How does high humidity affect the rate of transpiration

The lower the rate of humidity the faster the rate of transpiration

very dry conditions make the concentration ( diffusion ) gradient steeper so water loss is faster.

what happens to the plant if too much water is lost?

Plants will

• leaves will collapse and hang down reducing the surface area for water loss.

• Close stomata will stop water loss but also stop photosynthesis.

How to measure transpiration

A cut plant stem is sealed into the potometer using a rubber bung

The popometer acts like the xylem.

The when air bubbles are introduced to the capillary tube the distance the bubbles travel shows how much water the stem has taken up.

This gives and indirect measurement of the rate of transpiration.

formula for calculating the rate of transpiration?

rate of transpiration = distance travelled ÷ time in ( mins)