Plants MOCKS Flashcards
The cuticle
The cuticle is located outside the epidermis (made of wax) and protects against water loss
The palisade layer
Main site of photosynthesis and has long, narrow, tightly-packed (to capture as much light as possible) cells containing a lot of chloroplasts
The spongy layer
Main gas exchange surface of the leaf, absorbing CO2 and releasing oxygen and water vapour
Loosely packed cells with air spaces to allow gases to move in and out
The veins
help position the blade so that it is facing the light source
The stomata
They provide for the exchange of gases between the outside air and the branched system of interconnecting air canals within the leaf.
Roots
They keep plants securely in the ground and are covered with root hair cells which absorb water and nutrients from the soil.
Leaf function
produce food for the plant by photosynthesis
Stem function
to support the leaves; to conduct water and minerals to the leaves, where they can be converted into usable products by photosynthesis; and to transport these products from the leaves to other parts of the plant, including the roots.
role of xylem
transports water and mineral salts from the roots up to other parts of the plant
Mature xylem consists of
of elongated dead cells, arranged end to end to form continuous vessels
How are leaves adapted for photosynthesis
They are green because they contain lots of chlorophyll to absorb sunlight.
They have a large surface area to maximise the amount of sunlight they can absorb.
They are thin, allowing easy diffusion of gases into and out of the leaf.
They have veins (xylem and phloem) to allow the transport of water, mineral ions and glucose (food).
A waxy waterproof layer which reduces water loss, it is transparent to allow light through the leaf
How do root hair cells absorb water
Water is absorbed by the root hair cell by the preocess called, Osmosis. Water passes from a region of high water concentration (wet soil) through a semi-permeable membrane (the cell membrane) to a region of lower water concentration (the cytoplasm)
What is transpiration
Transpiration is the evaporation of water from the surface of a plant
How is rate of transpiration affected
Temperature
- evaporation and diffusion are faster at higher temperatures
Humidity
- diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air
Wind speed
- moving air removes water vapour, increasing the rate of diffusion of water vapour from the leaf
Light intensity
- the stomata open wider to allow more carbon dioxide into the leaf for photosynthesis
Equation for photosynthesis
6CO2 + 6H2O – C6H12O6 + 6O2
What does photosynthesis do
converts lights energy to chemical energy
How does light intensity affect the rate of photosynthesis
Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide and a suitable temperature.
Increasing the light intensity increases the rate of photosynthesis, until some other factor – a limiting factor – becomes in short supply.
How does temperature affect the rate of photosynthesis
The chemical reactions that combine carbon dioxide and water to produce glucose are controlled by enzymes. As with any other enzyme-controlled reaction, the rate of photosynthesis is affected by temperature.
At low temperatures, the rate of photosynthesis is limited by the number of molecular collisions between enzymes and substrates. At high temperatures, enzymes are denatured.
How does CO2 affect the rate of photosynthesis
Carbon dioxide – with water – is one of the reactants in photosynthesis.
If the concentration of carbon dioxide is increased, the rate of photosynthesis will therefore increase.
Again, at some point, a factor may become limiting
Geotropic responses of stems and roots
when the stem grows against the force of gravity, this is known as a negative geotropism
when a root grows in the direction of the force of gravity, this is known as a positive geotropism
in a root placed horizontally, the bottom side contains more auxin and grows less - causing the root to grow in the direction of the force of gravity.
The opposite happens in a stem. When a stem placed horizontally, the bottom side contains more auxin and grows more - causing the stem to grow upwards against the force of gravity.
Phototropic responses of stems and roots
Phototropism is a response to the stimulus of light.
Responses to stimuli of different parts of the plant
In the plant stem, responses to light are known as a positive phototropism, which means the stem grows towards the light
In the plant root, responses to light are known as a negative phototropism, which means the root grows away from the light
In a stem, the shaded side contains more auxin and grows longer, which causes the stem to grow towards the light. It is vital to note that the plant does NOT bend towards the light.
Auxins have the opposite effect on root cells. In a root, the shaded side contains more auxin and grows less - causing the root to bend away from the light.
Insect pollinated plants adaptations
- large and brightly coloured to attract insects
- scented and with nectar to attract insects
- sticky or spiky nectar grains to stick to insects well
- stigma is sticky so pollen grains stick when insect brushes past
Wind pollinated plants adaptations
- smooth and light pollen grains - easily carried by the wind without clumping together
- anthers are outside plant and are loose to release pollen easily
- stigma are outside plant and are feathery to make a network to catch drifting pollen grains
Growth of pollen tube
When a pollen grain lands on the stigma of a flower of the correct species , a pollen tube begins to grow. It grows through the style until it reaches an ovule inside the ovary. The nucleus of the pollen then passes along the pollen tube and fuses (joins) with the nucleus of the ovule.
