SB6-Plant structures and their functions Flashcards
What is photosynthesis?
When plants/algae trap energy from the sun (transferred by light) which is then transferred to glucose molecules
What does glucose store?
Energy
What is biomass?
The materials in an organism
What is the word equation for photosynthesis?
Carbon dioxide + water ~> glucose + oxygen
Where does photosynthesis occur?
Chloroplasts
Is photosynthesis an endothermic or exothermic reaction?
Endothermic as energy enters from the surroundings and the products have more energy than the reactants
What happens as glucose molecules are made?
They link together to form a polymer called starch
What happens when photosynthesis stops?
Starch is broken down into simpler substances which are moved into the cytoplasm and used to make sucrose
What is sucrose?
A sugar molecule that is transported around the plant
It is used to make starch, other molecules for the plant (eg proteins) and glucose for respiration
What adaptations allow leaves to absorb a great deal of light?
They are broad and flat resulting in a large surface area
The palisade cells near the top of the leaf contain lots of chloroplasts
What do stomata do?
They allow carbon dioxide to diffuse into the leaf
How do the stomata allow diffusion?
They are opened and closed by specialised guard cells
In the light water flows into pairs of guard cells which makes them rigid and opens the stoma
At night water flows out of the guard cells which makes them lose their rigidness and the stoma shuts
How are leaves adapted for diffusion?
They are thin which means carbon dioxide does not have to diffuse far before reaching the cells that need it
Does photosynthesis happen quicker at higher or lower temperatures?
Higher
What is a limiting factor?
A factor that prevents a rate increasing
What are limiting factors of photosynthesis?
Carbon dioxide concentration
Temperature
Light intensity
What is water absorbed by plant roots used for?
Carrying dissolved mineral ions
Keeping cells rigid
Cooling the leaves
Photosynthesis
What are root hair cells and how are they adapted?
Extensions of the cell that provide a large surface area to absorb water and mineral ions quickly
They also have thin cell walls so the flow of water into the cells is not slowed down
How does water pass into the cytoplasm of root hair cells?
Osmosis
How do water particles travel towards the middle of the root?
Diffusion
How do mineral ions enter root hair cells?
Active transport
What is transpiration?
The flow of water into a root, up the stem and out of the leaves
What keeps plants cool?
The evaporation of water from leaves
What are xylem vessels?
Tiny continuous pipes from a plants roots to its leaves
What is inside a xylem vessel?
An unbroken chain of water due to the weak forces of attraction between water molecules
What happens in xylem vessels?
Water is pulled up the xylem vessels in the stem as water evaporates from the xylem vessels in the leaves
As the water vapour diffuses out of a leaf more water evaporates from the xylem inside the leaf
What factors influence transpiration?
Any factor that reduces the concentration of water molecules outside the stomata
Eg:
Wind
Low humidity
Temperatures
Light intensity
What happens during xylem cells development?
Xylem cells die and their top and bottom cell walls disintegrate which creates long empty vessels through which water can move easily
Why are xylem vessels rigid?
They have thick side walls and rings of hard lignin so water pressure inside the vessels doesn’t burst or collapse them
It also helps to support the plants
Where is sucrose transported to?
The sieve tubes of the phloem tissue
How is sucrose transported in the sieve tubes of the phloem tissue?
The large central channel in each sieve cell is connected to its neighbours by holes which sucrose flows through
Companion cells actively pump sucrose into/out of the sieve cells that form the sieve tubes
As sucrose is pumped into sieve tubes the increased pressure causes the sucrose to flow up to growing shoots or down to storage organs
What does chlorophyll do?
It traps energy transferred by light
How do spongy cells allow diffusion?
They are irregularly shaped and do not fit together well which creates air spaces, allowing gases to diffuse easily inside a leaf
What do epidermis cells do?
They form outer layers of a leaf holding the leaf together and protecting the cells inside
How are epidermis cells adapted?
They are transparent to allow light to pass through them easily
They produce a waterproof waxy cuticle which prevents water loss and helps to stop microorganisms and water entering the leaf
How are plants adapted to cold conditions?
Plants lose their leaves in winter to prevent water loss
Conifers have stomata in small pits to trap water vapour close to their leaves- slowing the rate of diffusion out of the leaves
Some plants use tiny hairs to trap water vapour
How are plants adapted to dry conditions?
Cacti have spines instead of leaves to minimise the surface area of the plant and protect the stem from herbivores
Cacti stomata only open at night- carbon dioxide is taken in at night and stored for use during the day
Cacti stem store water
What is a stimulus?
A change in the environment that causes a response by an organism
What is a tropism?
Responding to a stimulus by growing towards or away from it
What is a tropism caused by light?
Phototropism
What is a positive tropism?
A tropism towards a stimulus
What part of plants are positively phototropic?
Plant shoots
What part of plants are negatively phototropic?
Plant roots
What causes positive phototropism?
The plant hormones auxins
Where are auxins produced?
The tips of a shoot
What do auxins cause in shoots?
Elongation of the cells
How do auxins work in shoots?
If a shoot is grown with light coming from only one direction, auxins move to the shaded side of the shoot
This makes the cells on the shaded side elongate more so the shoot grows towards the light
Where are auxins found?
Plant shoot tips and root tips
What do auxins cause in roots?
Cells to stop elongating- positive gravitropism
What does positive gravitropism do?
Helps roots to anchor the plant in place and reach moisture underground
What do gibberellins do?
Helps seeds to germinate and start to grow roots and shoots
What does ethene gas do in terms of plants?
Helps fruit to ripen
What do artificial auxins do?
Makes some plants grow uncontrollably which can kill them
How do selective weedkillers work?
They contain artificial auxins to kill plants with broad leaves (like dandelions) but not those with narrow leaves (like wheat)
This allows farmers to kill weeds in a wheat farm without harming the wheat
How do rooting powders work?
They contain auxins which cause plant cuttings to develop roots quickly
What is photoperiodism?
The response of an organism to the number of daylight hours in a day
What can gibberellins be used to do?
Override photoperiodism
Cause some plants to produce fruits without being pollinated which produces seedless fruits
Make plants produce bigger fruits
How can fruit producers use ethene?
Pick unripe fruit which is easier to transport without damaging and then ripen it when needed with ethene gas
This ensures fruit reaches shops in just-ripened conditions
