SB6 Plant Structures and their Functions Flashcards
Define Photosynthesis
A chemical process used by plants to make glucose and oxygen from carbon dioxide and water. It is an endothermic reaction
Define biomass
The materials in an organism
State the photosynthesis word equation
carbon dioxide + water –> glucose + oxygen
What chemical do plants contain which aids them to trap light for photosynthesis?
Chlorophyll contained in chloroplasts
What polymer do glucose molecules make?
Starch
What is the symbol equation for photosnythesis?
6Co2 + 6H20–> C6H12O6 + 6O2
Where does photosynthesis take place?
Plant leaves
What can starch be broken down into and what other molecules can be made?
Sucrose, which can be used to make cellulose, lipids or proteins
What are some adaptations of a leaf and what do they do?
- broad and flat (large surface area)
- thin (allows easy gas exchange)
- a network of veins (to support the leaf and transport mineral ions, water and sucrose)
- stomata (again allows gas exchange)
What are the parts of the leaf?
- spongy mesophyll
- cuticle
- veins
- guard cell
- stomata
- epidermis
- palisade
What is the role of the spongy mesophyll?
Layer with air spaces to increase surface area for gas exchange
What is the role of the cuticle?
- Waxy layer that prevents loss of water
- allows light through
- prevent infection from occuring
What is the role of the veins?
Made of tubes that carry water, minerals and sucrose in a plant
What is the role of the guard cell?
Controls the opening and closing of the stomata
What is the role of the stomata?
Pores in leaf that allow gases in and out
What is the role of the epidermis?
- A protective layer of cells that allows light through
- is thin and transparent
What is the role of the palisade?
Layer of cells with chloroplasts for photosynthesis
Define limiting factor
A factor that prevents a rate increasing
What are the limiting factors for photosynthesis?
- carbon dioxide concentration
- temperature
- light intensity
What equation is used to link distance and light intensity together?
light intensity is directly proportional to 1/distance^2
How does temperature affect photosynthesis?
- the reaction is controlled by enzymes so the temperature will continue to quicken the rate of reaction
- until the enzymes denature and the rate of reaction begins to decrease
How does light intensity affect photosynthesis?
- as there is more light to continue the reaction, more co2 and water can be made into glucose and oxygen
- so the rate of reaction increases
How does carbon dioxide concentration affect photosynthesis?
- also needed to make glucose, so if one of the products increases, so will the output
What is the water absorbed by plant roots used for?
- carrying dissolved mineral ions
- keeping cells rigid
- leaves cool due to evaporation
- photosynthesis
What are the adaptations of a root cell?
- Large surface area for water and mineral ions absorption
- thin cell walls so water can flow into cells easily
- lots of mitochondria as active transport has to take place for root hair cells to consume mineral ions
- found in tips of roots
What are root hair cells specialised for?
To take up water by osmosis and mineral ions through active transport
Define osmosis
When solvent molecules such as water diffuse through a semi-permeable membrane
What do plants need mineral ions for?
To produce new substances
Why do root hair cells need to use active transport to take in mineral ions from the soil?
- there is a larger concentration of mineral ions inside the root hair cells as compared to the soil
- so diffusion can’t occur into the root hair cell
- therefore energy has to be used to bring in more ions
Define transpiration
The flow of water into a root, up the stem, and out of the leaves; is an unavoidable side effect of photosynthesis
What happens during transpiration?
- plant opens its stomata to let in carbon dioxide
- water on the cell surfaces of the spongy mesophyll and the palisade mesophyll evaporate
- and diffuse out of the leaf
- as water molecules are attracted to each other when some molecules leave the plant the rest are pulled up through the xylem
- this results in more water uptake from the soil
- forming a continuous stream of water within the xylem vessels
What are xylem vessels and what is transported in them?
- tiny continuous pipes leading from a plant’s roots up to its stem
- transports water and mineral ions
What are the adaptations of xylem vessels?
- made up of ‘dead’ cells (hollow, no cytoplasm)
- lignin deposited in spirals which helps the cells withstand the pressure from the upwards movement of water
- cells that make up the xylem lose their end walls to form one continuous long tube
- lack of cell walls means the water speed remains unaffected
- tiny pores allow water and mineral ions to enter and leave
What is the purpose of transpiration?
- provides water for photosynthesis
- transports mineral ions
- cools the leaf as water evaporates
- provides water which keeps the cells turgid, supporting herbaceous plants
What factors affect transpiration?
- temperature
- air movement
- humidity
- light intensity
How does temperature affect the rate of transpiration?
- increases the rate
- increases molecular movement, which means that more water molecules evaporate from cell surfaces
–> The rate of diffusion from water molecules is increased
How does humidity affect the rate of transpiration?
- decreases the rate
- if humidity is high
- there will be a reduced concentration gradient between the water inside and outside the leaf
- which means the rate of diffusion slows down
How does air movement affect the rate of transpiration?
- increases the rate
- removes water vapour from surfaces of leaves
- forms a high concentration gradient
How does light intensity affect the rate of transpiration?
- increases the rate
- increases the rate of photosynthesis which means that the stomata are open for longer
- and water diffuses out of the leaf
Define translocation
The transportation of other minerals such as sucrose, it is an active process
Where does translocation occur?
Phloem cells
What are the cells that make up a phloem cell?
- sieve cells
- companion cells
What are the adaptations of a sieve cell?
- no nuclei for more space
- has a perforated end so one cytoplasm connects to the next
- only have some cytoplasm for space, therefore these cells are alive
What is the role of a companion cell?
- provides energy to the sieve cells
- pumps sucrose in and out of sieve cells
What adaptations do plants have for dry weather?
- rolled leaf, leaf hairs, stomata in pits: traps water vapour close to leaves which increases humidity + reduces water loss
- spines instead of leaves: less surface area for water loss
- thick cuticle: less water loss
- stomata open at night: less water loss through evaporation
What adaptations do plants have for cold weather?
- losing leaves: less water loss where the ground frozen
- needle-shaped leaves: same as above
What adaptations do plants have for tropical weather?
- large leaves: more surface area for photosynthesis
- tall plants: to obtain more sunlight
What adaptations do plants have for waterlogged conditions?
- no air spaces in soil: lack of oxygen
- more spongy tissue in root to store oxygen
Define stimulus
A change in the environment which causes a response by the organism
Define tropism
Responding to a stimulus by growing towards or away from it
What are the two main types of tropisms?
- positive tropism: plant grows towards the stimulus
- negative tropism: plant grows away from the tropism
What is the difference between gravitropism and phototropism
- phototropism: response to light
- gravitropism: responds to gravity
What are auxins?
Plant hormones which are used to respond to a stimulus, mainly made in the tips of roots and shoots but can diffuse to any place they are required
How do auxins respond to phototropism?
- positively
- when the plant is exposed to light on one side of the plant
- the auxins move to the shaded sides
- and stimulates the cells to grow there
- which makes the plant appear to bend towards the light
- since the plant receives more light, faster photosynthesis can occur
How do auxins in the shoots of plants respond to gravitropism?
- negatively
- if a shoot is horizontal:
- auxins move to the lower side
- the cells of the auxins grow more on the side with more auxins so more cells grow
- which makes the plant grow away from the ground
- this is beneficial because it allows the plant to gain more light for photosynthesis
How do auxins in the roots of plants respond to gravitropism?
- positively
- if a root is horizontal
- auxin moves to the lower side
- cells of the root grow more on the side with less auxins so it stimulates cells to grow on the upper side
- which makes the root bend and go downwards
- beneficial as more water may be available and helps roots to anchor the plant
How do auxins in the roots differ from those in the shoots?
- in the shoots, wherever the auxins go they cause elongation of the cells
- whereas in the roots they stop cell elongation
How are artificial auxins used?
- selective weedkillers: can kill weeds with broad leaves, which are the majority of them
- rooting powder: increase the development of roots in cuttings
- gibberellins (released during seed germination) can trigger artificial germination
- ethene is a plant hormone which can be sprayed to prevent early ripening
