SB6: plant structures and their functions Flashcards
photosynthesis
a chemical process used by plants to make glucose and oxygen from carbon dioxide and water, using light energy
photosynthesis chemical equation
6CO2 + 6H20 —> C6H1206 + 602
photosynthesis word equation
carbon dioxide + water — sunlight—> glucose + oxygen
what type of reaction is photosynthesis? (endo/exo)
endothermic
endothermic
energy taken in
exothermic
releases energy
what is the main organ for photosynthesis?
leaves
where do the reactants of photosynthesis come from?
carbon dioxide:
-from the air
-enters the leaves through the stomata
water:
-from soil
-enters through roots
-transported to leaves in the xylem
what is the oxygen made by photosynthesis used for?
- respiration
-some plants and algae give out oxygen if the photosynthesis rate was high
what is the glucose made by photosynthesis used for?
respiration
why is glucose important for plants?
-starch (many glucose molecules joined)
-cellulose (many glucose molecules joined)
-lipids
how can the rate of
photosynthesis be measured?
-the rate of oxygen production
-the rate of carbon dioxide uptake
-the rate of glucose production
what factors affect photosynthesis?
-light intensity
-temperature
-carbon dioxide concentration
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
-increasing the light intensity increases the rate of photosynthesis, until some other factor - a limiting factor - becomes short in supply
-the rate of photosynthesis is directly proportional to the light intensity (until another factor becomes limiting)
-at very high light intensities, photosynthesis is slowed, but these light intensities do not occur in nature
how does carbon dioxide affect the rate of photosynthesis?
-carbon dioxide is one of the reactants in photosynthesis
-if the concentration of carbon dioxide is increased, the rate of photosynthesis will increase
-at some point, another factor may become limiting
how does temperature affect the rate of photosynthesis?
-the chemical reactions involved in photosynthesis are controlled by enzymes
-as with any other enzyme-controlled reaction the rate of photosynthesis is affected by temperature
-as temperature increases the number of collisions increases, therefore the rate of photosynthesis increases, however, at high temps, enzymes are denatured and this will decrease the rate of photosynthesis
how carbon dioxide concentration affects photosynthesis?
-the higher the carbon dioxide concentration, the faster the rate of photosynthesis is
light intensity and photosynthesis practical: method
- a lamp with an LED bulb (won’t change temperature) is set up at different distances from the plant (pondweed) in a beaker of water
- sodium hydrogen carbonate is added to the water to supply the reactant carbon dioxide to the plant (pondweed)
- the bubbles produced over one minute periods are recorded (the rate of photosynthesis)
light intensity and photosynthesis practical: variables
independent variable: distance from the light source/light intensity
dependent variable: the number of bubbles produced per minute
control variables - concentration of sodium hydrogen carbonate solution, temperature, using the same size/piece of pondweed each time
light intensity and photosynthesis practical: risks
-care must be taken when using water near electrical equipment
-ensure that your hands are dry when handling the lamp
light intensity and photosynthesis:
extension activities
-the volume of oxygen produced could be measured by collecting the gas produced in a gas syringe
-you could investigate the effect of different wavelengths of light on photosynthesis -> use coloured acetate filters to investigate the effects of the blue, green and red parts of the spectrum on photosynthesis
direct proportion
the relation between quantities whose ratio is constant
inverse proportion
a relation between two quantities such that one increases in proportion as the other decreases
inverse square law
light energy is inversely proportional to the square of the distance of the light source from the plant
eg: 2d = 1/4 light intensity (light intensity at
twice the distance away is spread over four times the area
structure of a flowering plant
flower, leaf, stem, roots
leaf features:
large surface area:
-to absorb more light
thin:
-short distance for carbon dioxide to diffuse into cell
chlorophyll:
-absorbs sunlight to transfer energy into chemicals
network into veins:
-to support the leaf and transport water and sugars
stomata:
-allow carbon dioxide to diffuse into the leaf and oxygen to diffuse out
internal structure of the leaf
1) waxy cuticle:
-to protect the leaf from infection and retain water without blocking out light
-thin
2) upper epidermis:
-thin & transparent to allow more light to reach the palisade cells
3) palisade mesophyll
-to absorb more light and increase the rate of photosynthesis
-contains many chloroplasts to absorb all the available light
4) spongy mesophyll
-air spaces allow carbon dioxide to diffuse through the leaf
5) lower epidermis & guard cells
-protective layer of cells, produces a waxy cuticle too in some plant species, contains stomata
(6. waxy cuticle)
biomass
dry mass of an organism
how is water loss reduced in plants?
-waxy cuticle to stop the water vapour escaping through the epidermis
-fewer stomata on their top surface to reduce water loss
xylem
-narrow, hollow tubes with lignin (gives strength and support to the plant)
-move water and mineral ions from the roots to the leaves
-consists of dead cells which lose their end walls so the xylem forms a continuous, hollow tube
phloem
-moves food substances produced in photosynthesis like sucrose and amino acids from leaves to the rest of the plant
-transport is up and down the stem (translocation)
what living cells does the phloem consist of?
sieve tubes:
-specialised for transport, have no nuclei
-each has a perforated end so its cytoplasm connects one cell to the next
-sucrose and amino acids are translocated in living cytoplasm of the sieve tubes
companion cells:
-transport of substances in the phloem needs energy
-1+ compcells attach to each sieve tube to provide this energy
-a sieve tube is dependent on its companion cell
gas exchange in leaves
carbon dioxide moves from the air into the leaf while oxygen moves out of the leaf through the stomata
translocation
the transport of dissolved material within a plant
root hair cells (how they absorb things, description)
-cells with long hairlike extensions that increase the surface area for the absorption of water and minerals from the soil
-absorb water from the soil by osmosis
-absorb mineral ions by active transport
why do root hair cells have lots of mitochondria?
to release lots of energy for the active transport of minerals and ions from the soil
stomata
-tiny holes found in the underside of leaves
-they control water loss and gas exchange by opening and closing
-they allow water vapour and oxygen out of the leaf and carbon dioxide into the leaf
how is the size of the stomata controlled?
guard cells
plants in dry environments
tend to have small numbers of tiny stomata and only on their lower leaf surface, to save water loss
role of guard cells
-control opening and closing of stomata to prevent water loss
-in bright light the guard cells take in water by osmosis and become plump and turgid, in low light the guard cells lose water and become flaccid, causing the stomata to close
-they would normally only close in the dark when no carbon dioxide is needed for photosynthesis
transpiration
-the loss of water from leaves by evaporation (through the stomata)
-transpiration is an unavoidable consequence of photosynthesis
how is transpiration regulated?
-water is drawn from the xylem to replace the water that has been lost from the leaves.
-water molecules inside the xylem cells are strongly attracted to other water molecules, there is strong cohesion between the molecules because of hydrogen bonding
-a continuous column of water is therefore pulled up the stem
-as water travels through the xylem in the stem and leaf, it is being replaced by water taken up by the roots
how temperature affects transpiration
the warmer it is, the faster transpiration happens, water particles have more energy to evaporate and diffuse out of the stomata
how humidity affects transpiration
if the air outside the leaf is very dry, then the concentration gradient between the water vapour inside and outside the leaf is steeper than if it were humid, so water vapour diffuses out of a leaf at a faster rate in dry conditions, resulting in faster transpiration
how air movement affects transpiration
removes water vapour from leaf surfaces; more water diffuses from the leaf because a high concentration gradient is maintained
how light intensity affects transpiration
plants close their stomata in the absence of light when photosynthesis cannot occur, preventing transpiration from occurring & vice versa
measuring water uptake with potometers
1) the potometer is filled with water
2) a shoot is cut from a plant
3) the end of the shoot is cut under water to ensure the xylem remains water-filled and prevents air locks
4) the shoot is inserted into the rubber tubing at the end of the potometer
5) the potometer is raised so that a bubble of air is taken up
6) the potometer is lowered into the water. the distance travelled by the air bubble is recorded over a period of time
rate (potometer)
distance/time
how cacti are adapted
-stems that can store water
-widespread & very deep root systems that can collect water from a large area or from very deep underground
-spines which are modified leaves that minimise the surface area and so reduce water loss, the spines also protects the cacti from animals that might eat them
-very thick, waxy cuticle to reduce water loss by evaporation
-reduced number of stomata to reduce water loss by transpiration
tropism
plant growth in response to a stimulus
postitive & negative tropisms
positive:
-plant grows towards stimulus
negative:
-plant grows away from stimulus
phototropism
a growth in response to light
what are auxins?
plant hormones that change the rates of elongation in plant cells and control growth of stems and roots
-allow growth in stem
-inhibit growth in roots
phototropism in stems
-positive phototropism, stem grows towards the light
-auxin causes the cells to elongate on the shaded side & grow towards the light
phototropism in roots
-negative phototropism, root grows away from the light
-the shaded side contains more auxin and grows less, the root to bend away from the light
gravitropism
a growth response to gravity
gravitropism in stems
-negative gravitropism
-when a stem is placed horizontally, the bottom has more auxin and grows more, the stem to grow up against the force of gravity
gravitropism in roots
-positive gravitropism
-in a root placed horizontally, the bottom side has more auxin and grows less, the root to grow in the direction of the force of gravity
how is auxin used to kill weeds?
-contains a growth hormone that causes the weeds to grow too quickly and die
-because the weeds have broader leaves, the weed killer is absorbed in larger quantities by the weeds than it is by the grass
how is rooting powder used on cuttings?
contains plant hormones into which cuttings are dipped to speed up the growth of new roots
what are giberellins?
-group of plant hormones responsible for growth and development
-initiate seed germination
how do gibberellins cause stem elongation?
they stimulate cell elongation so plants grow taller
how do gibberellins end seed dormancy?
-gibberellins break seed dormancy to make seeds germinate
-they promote seed flowering
how does ethene help with ripening fruit?
-ethene is a hydrocarbon gas which speeds up ripening in fruit
-it controls cell division during plant growth
-fruit is often picked unripe and then transported
-this prevents fruit from over-ripening on the journey
-it is ripened during storage by adding ethene and then taken to the shops
