Topic 6: Plant Structure & Function Flashcards
What is photosynthesis?
An endothermic reaction that happens in plants and algae, in which energy is transferred to chloroplasts from the environment by light
What is the equation for photosynthesis?
Carbon + water —light—> glucose + oxygen
Is photosynthesis endothermic or exothermic?
Endothermic
Where does photosynthesis occur?
In the chloroplast
What do photosynthetic organisms make?
Biomass out of glucose
Who are the main producers of food for nearly all life on earth?
Photosynthetic organisms - they produce their own biomass
What is a limiting factor of photosynthesis?
A thing that stops photosynthesis happening faster
What are 3 limiting factors for photosynthesis?
- Temperature
- CO2 concentration
- Light intensity
How is temperature a limiting factor of photosynthesis?
Enzymes work slowly at low temperatures so photosynthesis slows down
High temperatures can also denature enzymes involved in photosynthesis
How are rate of photosynthesis and light intensity proportional?
Directly proportional
How are rate of distance from light source and light intensity proportional?
Inversely proportional
What is inverse square law?
Light intensity ∝ 1/distance²
In relation to the inverse square law, what happens if the distance from light source is doubled?
Light intensity becomes 4 times smaller
How does a light intensity limiting factor graph look like?
The line is straight and then plateaus
How does a CO2 concentration limiting factor graph look like?
The line is straight and then plateaus
How does a temperature limiting factor graph look like?
The line is not steep and is straight then curves and the rate decreases rapidly
What types of cells to plant root cells have?
Root hair cells
What are properties of root hair cells?
Large surface area - allows for more efficient absorption
Thin cell wall - allows for a short path for water and minerals
Many mitochondria - provides energy for active transport
What do root hair cells absorb, through what process?
Absorb mineral ions and water - through active transport
What are stomata?
Pores that let gases and water vapour escape from a plant
What are the role of the stomata?
Control gas exchange in the leaf
Limit evaporation and water loss
When does a stomata close?
When guard cells go flaccid
What are stomata surrounded by?
Guard cells
What do stomata do when they’re open?
They take in water through osmosis - changes in their shape
What controls the opening and closing of the stomata?
Guard cells
What is a xylem?
A tissue that carries water in the transpiration streams
What are properties of the xylem?
Walls are made of lignin - stops the xylem from bursting
Has no end walls - so water can travel up by capillary action in transpiration stream continuously
Made up of dead cells
Where does the xylem transport water from and to?
From: roots
To: stem and leaves
In the xylem, what direction does water flow?
ONLY up
In the phloem, what direction does sucrose and other food substances flow?
BOTH up and down
What does a xylem transport?
Water and mineral ions
What does a phloem transport?
Sucrose and other food substances
What are properties of the phloem?
They have small pores in end walls - to let substances through
They’re made up elongated living cells
Where does the phloem transport sucrose from and to?
From: leaves
To: rest of the plant
Why do plants carry out translocation through the phloem?
They need sugars like sucrose distributed throughout the plant for respiration
When food molecules, like sucrose, are transported, what happens to them?
They can be used immediately or stored
What is translocation?
The process in which food is moved through the phloem tubes, it requires energy
What is transpiration?
The loss of water from a plant
What is the process of transpiration?
- The water moves into the root by osmosis, up the stem through the xylem vessels to the leaves
- It then evaporates out of the leaf - done by capillary action
Why is transpiration important?
Cools plant
Pumps water and minerals to the leaves for photosynthesis
What are the 4 factors that increase the rate of transpiration?
- High light intensity
- Warm temperature
- Dry conditions (not humid)
- Good air flow
How does high light intensity increase rate of transpiration?
Stomata is open when it’s light - water diffuses out of the leaf faster
How does warm temperature increase rate of transpiration?
Water molecules have more kinetic energy - evaporation and diffusion rate increases
How do dry conditions increase rate of transpiration?
Diffusion of water from the leaf increases - because the conditions outside the plants have a low concentration of water
How does good air flow/wind increase rate of transpiration?
Fewer water molecules surround the leaves - so there’s a higher water concentration inside the leaf than outside and diffusion occurs faster
What is a potometer?
A piece of equipment that measures the rate at which transpiration occurs
How to calculate the rate of transpiration from a potometer?
Transpiration rate = distance moved by bubble/time taken
How does a potometer work?
- Water flows through a capillary tube to a plant that takes up water
- Air is then taken and the air bubble within the potometer moves
- The distance this bubble travels can be used to estimate the rate
What are the 8 adaptations of plants for photosynthesis and gas exchange?
- Cells in the upper epidermis
- Chloroplasts in the palisade mesophyll
- Air spaces in the spongy mesophyll
- Stomata in the lower epidermis
- Phloem
- Xylem
- Broad shape
- Waxy cuticle
How are cells in the upper epidermis adapted for photosynthesis?
They’re transparent - let light through for photosynthesis
How are chloroplasts in the palisade mesophyll adapted for photosynthesis?
There’s a lot of the chloroplasts - rate of photosynthesis increases as there’s lots of light in the palisade mesophyll
How are air spaces in the spongy mesophyll adapted for gas exchange?
There are a lot of air spaces - allows for a faster diffusion of gases
How are stomata in the lower epidermis adapted for gas exchange?
There’s a lot of them in the lower epidermis - allows gases to go in and out of the plant
How is the broad shape of the leaf adapted for photosynthesis?
Broad shape - has a large surface area - allows for more exposure to light - increases rate of photosynthesis
How is the waxy cuticle adapted for the leaf?
It reduces water loss
What is a xerophyte?
A plant adapted to living in dry conditions
Examples of xerophytes?
Cacti
Marram grass
What are the 5 adaptations of xerophytes?
- Small leaves or spines
- Curled leaves or hairs on leaves
- Thick, waxy cuticle
- Stomata in pits
- Stomata only open at night and are shut during the day
How do small leaves or spines on xerophytes help reduce water loss?
Reduces surface area - less water evaporates
How do curled leaves or hairs on leaves on xerophytes help reduce water loss?
They trap water vapour - reducing diffusion from leaf to air
How does a thick, waxy cuticle on xerophytes help reduce water loss?
Less water can evaporate as even more water is prevented from passing through the epidermis
How do stomata being in pits in xerophytes help reduce water loss?
Reduce air flow near stomata - reducing diffusion of water vapour from the leaf to air
How do stomata being closed during the day in xerophytes help reduce water loss?
It’s warmer in the day so more evaporation and transpiration will occur in the day - shutting stomata in day reduces this loss
What is an auxin?
A plant hormone that controls growth near the tips of shoots and roots
Are shoots positively or negatively phototropic? Describe process
Positively phototropic
- Shoot exposed to light
- Auxin accumulates on the shaded side
- Shoot bends towards the light
- Cells can grow faster on the shaded side because of this
CELL ELONGATION
Are roots positively or negatively phototropic? Why?
Negatively phototropic - grow away from light
What does positive phototropism mean?
Growing towards the direction of light
What does negative phototropism mean?
Growing away from the direction light
Are shoots positively or negatively gravitropic? Describe process
Negatively gravitropic
- Auxin accumulates on the lower side of the shoot
- Auxin makes the lower side of the shoot grow quickly
- Shoot bends upwards
Are roots positively or negatively gravitropic? Describe process
Positively gravitropic
- Auxin accumulates on the lower side of the root
- Auxin inhibits the root growth on the lower side of the root
- Root bends downwards
What is positive gravitropism?
Growing downwards in the direction of gravity (since gravity acts downwards)
What is negative gravitropism?
Growing upwards against the direction of gravity (since gravity acts downwards)
What are the 3 plants hormones that are commercially used?
- Auxins
- Ethene
- Gibberellins
What are the commercial uses of auxins?
Developed to selectively kill weeds whilst crops remain untouched
Added to rooting powders to promote root growth in plant cuttings
What are the commercial uses of ethene?
Speeds up the ripening of fruits - used in the transporting of fruits to shops
What are the commercial uses of gibberellins?
Stimulates seed to germinate at any time of the year
Induces flowering without need for specific conditions
Reduces number of fruits produced - each fruit can grow larger
Can make un pollinated flowers produce seedless fruits
EFFECT OF LIGHT INTENSITY ON RATE OF PHOTOSYNTHESIS CORE PRACTICAL: What are the steps to this experiment?
- Set up the apparatus: beaker with water and pondweed (photosynthesises and produces oxygen) in it that has a bung on it, a gas syringe connected to the beaker
- Have a light source 25cm away from the flask
- Measure the volume of oxygen produced in 2 minutes using a stop clock
- Repeat steps 2-3 again but bring the light source 5cm closer each time (USE A RULER TO MEASURE THIS DISTANCE)
EFFECT OF LIGHT INTENSITY ON RATE OF PHOTOSYNTHESIS CORE PRACTICAL: How can the rate of photosynthesis be calculated from this experiment?
Rate = volume of oxygen produced/time
EFFECT OF LIGHT INTENSITY ON RATE OF PHOTOSYNTHESIS CORE PRACTICAL: What is the conclusion of this experiment?
The higher the light intensity (closer the the light source to the pondweed), the faster rate of photosynthesis and thus faster rate of oxygen produced
EFFECT OF LIGHT INTENSITY ON RATE OF PHOTOSYNTHESIS CORE PRACTICAL: What are the control, independent and dependent variables?
Control: the light source used, mass of pondweed, volume of water
Independent: distance of light source/light intensity
Dependent: volume of oxygen produced
