Plant structures and their functions

Why are plants called producers?

They produce their own food via photosynthesis

What is biomass

The mass of a living material at a particular stage in a food chain

What is the equation for photosynthesis?

Carbon dioxide + Water → Glucose + Oxygen

What energy transfer is there in photosynthesis?

There in an energy transfer of light energy to chemical energy stored in the sugars produced

What are four limiting factors of photosynthesis?

Low temperature, dim light and low carbon dioxide concentration all limit the rate of photosynthesis, amount of chlorophyll

How does light intensity and carbon dioxide concentration affect the rate of photosynthesis?

• If there is a low amount light intensity or carbon dioxide the rate of photosynthesis will be slower

• If there is a high light intensity or carbon dioxide the rate of photosynthesis will be higher

What is happening when either increasing the light intensity or carbon dioxide amount does NOT increase the rate of photosynthesis?

• When either of these factors are high the rate of photosynthesis will not increase because another factor is limiting it from increasing

• In this case, temperature would be the limiting factor

How does temperature affect the rate of photosynthesis?

• Photosynthesis is an enzymes controlled reaction

• When the temperature is low, the molecules and enzymes are moving slower because they have little kinetic energy

• Increasing the temperature increases the kinetic energy of the molecules and enzymes, causing them to move faster and hit harder

• This increases the rate of photosynthesis as there are more successful collisions

• At high temperatures, enzymes involved is digestion and synthesis can be denatured, slowing down the rate of photosynthesis

What happens in temperature gets too high for photosynthesis?

• If the temperature is too high, enzymes will begin to denature

• This decreases the rate of photosynthesis

How are phloem in plants specialised to carry out their function?

• Contains sieve tube elements which have very little cytoplasm- this maximises the space for the transport of sucrose and nutrients

• Contains companion cells which have lots of mitochondria- these supply energy from respiration for active transport of sucrose into and out of the sieve tubes

How are xylem vessels in plants specialised to carry out their function?

• These are dead cells which have no cytoplasm or cell contents- there is more space for water containing mineral ions

• They have holes called pits in their walls to allow water and mineral ions to move out

• Walls are strengthened with lignin rings making them very strong and prevents them from collapsing

• They have no end walls so they form a long tube letting water flow through easily

What is transpiration?

The loss of water by evaporation from the leaves of a plant

What is the movement of water from the roots to the leaves of a plant called?

The transpiration stream

Where are stomata found?

On the lower surface of the leaf

How do stomata work in plants?

• They are surrounded by a pair of sausage shaped guard cells

• When guard cells take in water they swell causing the stomata to open

• When guard cells lose water, they become flaccid and the stomata closes

• They close at night because photosynthesis can’t take place, this reduces loss of water

What are the steps of transpiration?

• Water enters the roots by osmosis

• Water is transported up the stem through the xylem vessel

• Water is drawn out of the leaf cells and xylem

• Water evaporates from leaves mainly through the stomata

What is translocation?

The transport of sucrose around a plant

What does the phloem transport?

Dissolved sugars

Which direction does water move in transpiration?

Up

Which direction does sucrose move in translocation?

Up and down the plant

What are the steps of translocation?

• Sucrose is produced in leaves from glucose formed during photosynthesis

• Dissolved sucrose is carried around the plant in phloem

• Dissolved sucrose is needed for growth in growing regions

• Dissolved sugars are also turned into starch and stored in storage organs for later use

How is a leaf adapted for photosynthesis?

• Waxy cuticle on surface and epidermis cells are transparent to let light through

• Palisade mesophyll cells are packed with chloroplasts and near the upper surface of the leaf, maximising photosynthesis

• Xylem brings water for photosynthesis

• Phloem removes sugars made in photosynthesis

• Flattened shape of leaf gives a large surface area

How is a leaf adapted to gas exchange?

• Air surrounds most of the surface of each cell so that gas exchange can take place over most of the surface

• Internal air spaces increase surface area for diffusion of gases

• Flattened shape of leaf gives a large surface area

• Stomata allow carbon dioxide from air to enter the leaf and allow oxygen from photosynthesis to leave the leaf

How does light intensity affect transpiration?

• High light intensity causes stomata to open- this causes the plant to lose water

• This increases the rate of evaporation of water from the leaf so more water is taken up to replace this

How does air movement affect transpiration?

• Wind blows moist air away from stomata, keeping the diffusion gradient high

• The more air movement there is, the higher transpiration rate

How does temperature affect transpiration?

• When temperature is high, water molecules have more energy

• They move faster, increasing the rate of transpiration

How can a potometer be used to measure the rate of transpiration with this equipment?

1. Note the position of the bubble on the ruler at the start of the investigation

2. Note the position of the bubble after a known number of minutes

3. Use the equation distance moved/time taken to find the rate of transpiration

What is one example of a plant that has adapted to hot and dry conditions in a desert?

Marram grass

How is marram grass adapted to living in a desert?

• Stomata sunk in pits to reduce water loss

• Waxy cuticle reduces water loss

• Rolled leaf to reduce air movement around stomata so less water is lost

• Leaf hairs to trap moist air around stomata

How do some plants adapt to tropical conditions where it is wet and has low light intensity?

• Large leaves to take in as much light as possible

• Stems and leaves that climb up trees to obtain more light, with the plant’s roots still in the ground

• Leaves with ‘drip tips’ so water runs off them

How are some plants adapted to waterlogged soil?

• Waterlogged soil has no air spaces so root hairs have difficulty obtaining oxygen for respiration

• Some plants have spongy tissue in their roots that store oxygen

• Fine surface roots that take in oxygen at the water surface

What is a tropism?

A plant’s response to stimulus (a change in the environment) by growing

What is phototropism?

Plants shoots growing towards light

What is gravitropism?

Plant roots growing downwards, towards the pull of gravity

What are auxins and what do they do?

• Auxins are plant hormones that causes cells to grow longer

• They are affected by light and cause phototropism in shoots and gravitropism in roots

How do auxins work?

• In a shoot, auxins are produced near the top of a shoot

• When light hits the shoot the auxins move to the shaded side of the shoot

• The shoot then bends towards the light

• In gravitropism auxins cause the root to grow downwards, away from light and towards gravity

Why does phototropism happen in plants?

So they can get more sunlight for photosynthesis

Why does gravitropism happen in plants?

When the shoots move further down they are able to reach more water and nutrients as well as anchoring themselves which provides stability

What is another name for gravitropism?

Geotropism

How are auxins used in selective weedkillers?

• Weed plants compete with crop plants for water and minerals from the soil

• Weed plants have broader leaves then crop plants

• Broad-leaved plants absorb more of the auxins causing uncontrollable growth, eventually killing the plant

• Crop plants get more minerals and water, so they grow better

What is rooting powder and how is it used?

• Gardeners take cuttings of plants to grow into new plants

• They dip the stalk end into rooting powder

• This contains auxins that cause the stalk to produce roots faster, helping the cuttings to grow into fully developed plants

How are gibberellins used by humans?

• Gibberellins stimulate germination of seeds, increasing crop yields

• They also stimulate flower and fruit production, again increasing the yield

• They stimulate stem elongation- when done on crops like sugar cane, this increases it’s yield

• They can be sprayed on flowers to produce seedless fruit

• They make fruit grow larger

How do humans use ethene for plants?

• Ethene hastens the ripening of fruit

• If you transport fruits you can transport them as unripe and then use ethene to ripen them

• This means that the fruit will not be too unripe to be sold