Photosynthesis Flashcards
What is the equation for photosynthesis? (not word)
6CO2 + 6H20 -> C6H1206 + 6O2
What type of reaction is photosynthesis?
Endothermic and enzyme-controlled
Why are plants called producers?
Because they produce their own food and therefore biomass
What is biomass?
The mass of living material at a particular stage in a food chain
What is light energy transferred into?
Into chemical energy stored in the sugars produced
What is chlorophyll?
The green pigment found inside the chloroplasts of leaves which absorbs sunlight
What colour does hydrogen carbonate indicator turn when in low levels of CO2?
Purple
What colour does hydrogen carbonate indicator turn when in high levels of CO2?
Yellow
What colour does hydrogen carbonate indicator turn when in the same levels of CO2 in normal air (0.035%)?
Orange-red
What relationship is between light intensity and distance from a lamp?
Inverse square relationship
What are some limiting factors?
- Concentration of CO2
- Access to water
- Wavelength of light
- Light intensity
- Temperature
- Chlorophylic content
Why is temperature a limiting factor?
Because it increases the kinetic energy of molecules and increases the rate of enzyme activity, making the process faster
What happens if the temperature is too high?
Enzymes start to denature and therefore the rate of photosynthesis slows down
Why is photosynthesis an endothermic reaction?
Because the products of the reaction have more energy than the reactants
What is sucrose used to make in plants?
Starch, cellulose and glucose for respiration
What does a high concentration of palisade cells and a large surface area for leaves mean for plants?
They allow a leaf to absorb a great deal of light for photosynthesis
What are stomata?
Microscopic pores in leaves that are opened and closed by specialised guard cells
Describe how guard cells open and close the stoma
- In the light, water flows into the guard cells making them rigid, which opens the stoma
- At night in the dark, water flows out of the guard cells where they lose their rigidity and shut
What do stomata allow for oxygen?
For it to be released into the air as well as water vapour
What does the algal ball experiment test for?
By placing the algal balls in hydrogen carbonate indicator, levels of CO2 are identified (yellow=high, purple=low). The algal balls are placed at different distances from a lamp, and CO2 is produced due to photosynthesis (the closer the bottle to the lamp, the greater the concentration of carbon dioxide)
What is the control variable in the algal balls experiment?
The volume of indicator solution and number of algal balls in each bottle
What is the dependent variable in the algal balls experiment?
The colour of the solution of the pH range bottles
What is the independent variable in the algal balls experiment?
The distance of each bottle from the lamp
What experiment can help show the effect of light on the rate of photosynthesis?
- Algal balls experiment
- Measuring the rate at which oxygen is given off by a piece of pondweed
What can greenhouse farmers use so that photosynthesis can continue beyond daylight hours or in higher-than-normal light intensity?
Artificial light
Why do leaves have a large surface area?
For the absorption of sunlight for photosynthesis and for gas exchange through the stomata
What is the inverse square law for light intensity?
Light intensity ∝ 1/d^2
What is a photochemical reaction?
A chemical reaction caused by the absorption of light
What are substomatal air spaces?
Large internal spaces inside leaves which increase the SA for the diffusion of gases
How are epidermis cells adapted?
They are transparent to let light pass through to the photosynthetic cells
How is a waxy cuticle an adaptation for a leaf?
It is transparent to let light through
How are mesophyll cells adapted?
They are packed with chloroplasts for maximum photosynthesis
How are xylem vessels adapted?
They carry water and mineral ions up the plant for photosynthesis
How are palisade mesophyll cells adapted?
They are packed with chloroplasts near the upper surface of the leaf for maximum reach of sunlight for photosynthesis
How are stomata adapted?
They are pores that allow CO2 from the air into the leaf and allow oxygen from photosynthesis to leave the leaf
Describe the arrangement of stoma thickness
- The cell wall of the guard cell is thicker on the side which borders the stoma
- As water is taken into the guard cell they become more turgid and (because of the uneven distribution of cellulose) they become more curved and the stomatal pore between them open
What do the veins do in leaves?
They carry water to the cells and carry glucose away; they also support leaves
Where are stomata mainly found?
In the lower surface of the leaf
How do guard cells take in water?
By osmosis
What are adaptations to dry conditions that marram grass have?
- Stomata sunk in pits to reduce water loss
- Waxy cuticle to reduce water loss
- Leaf hairs to trap moist air round stomata
- Rolled leaves to reduce air movement around stomata
What are adaptations that plants have to tropical conditions?
They adapt for low light intensity and wet conditions:
- Large leaves that absorb as much light as possible
- Stems that climb up the trees to obtain more light, with the plant’s roots still in the ground
- Leaves with ‘drip tips’ so water runs off them
- Cuticle of leaves have water repelling properties so that they are ‘self-cleaning-
What are adaptations plants have to waterlogged soil?
Waterlogged soils have no air spaces so the root cells have difficulty obtaining enough oxygen for respiration:
- Spongy tissue in their roots that stores oxygen
- Fine surface roots that take in oxygen at the water surface
What are pneumatophores?
They are specialised root structures that grow out from the water surface and facilitate the aeration necessary for root respiration trees (like the mangrove)
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 phototropism?
A tropism caused by light
What is a positive tropism?
A tropism towards a stimulus
What types of tropism are plant roots and shoots?
Shoots - positively phototropic
Roots - negatively phototropic
How do plants respond to stimuli?
Using plant hormones
What hormone is positive phototropism caused by?
Auxins
What are auxins?
Plant hormones that are produced in the tips of a shoot, where they cause the elongation of cells
What do auxins do the speed of shoots and roots?
- Slow down roots
- Speed up shoots
How does cell elongation work?
- 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, which in turn causes the shoot to grow towards the light
Which scientist was one of the 1st to work out what was going on when plant shoots bend towards the light?
Charles Darwin
What is Went’s conclusion about the bending of light supported by?
The extraction and purification of auxins
What is positive gravitropism?
Growth towards the direction of gravity
What causes positive gravitropism?
When auxins cause cells to stop elongating in roots and instead grow downwards towards direction of gravity
What does positive gravitropism help with?
Helps roots to anchor the plant in place and to reach moisture underground
What are gibberellins?
Plant hormones that helps seeds germinate and start to grow roots and shoots (without fertilisation)
What is ethene gas?
A plant hormone that help fruit to ripen
What are selective weedkillers?
Substances that contain artificial auxins to kill plants with broad leaves, but not those with narrow leaves (kills weed without affecting the crop)
Where can auxins be found?
In rooting powders
What can root powders help with?
Auxins in them can cause plant cutting to develop roots quickly, where large numbers of identical plants can be produced quickly using cuttings compared to growing plants from seed
What do gibberellins help plant growers with?
Allows seeds to germinate without the standard period of darkness/cold needed
What is photoperiodism?
The response of an organism to the number of daylight hours in a day
How can flower growers override photoperiodism?
By spraying the plants with gibberellins
What can gibberellins help produce?
Seedless or bigger fruits
How are seeded fruits produced?
They produce seeds after being pollinated, which then allows egg cells to be fertilised and seeds to form
Why are unripe fruits better to transport without damaging them?
They can be kept for longer in cold storage without going off
What does ethene gas help fruit with for the market?
They are kept unripened in cold storage until the fruit reaches the shops where they are treated with ethene gas to ripen them, so they are in a ‘just-ripened’ condition
What is transpiration?
The loss of water by evaporation from leaves
What is the force between water molecules like inside of a xylem vessel?
There is an unbroken chain of water due to the weak forces of attraction between water molecules
Where is the concentration of water vapour greatest in a leaf?
Greater inside than out
What does a bigger difference of water concentration between inside and outside the leaf mean?
A steeper concentration gradient, and so diffusion happens faster
What factors increase the rate of transpiration?
Wind (moves water molecules away from the stomata) Low humidity (little vapour in the air)
How do xylem vessels develop?
- Xylem cells die and their top and bottom cell walls disintegrate
- This creates a long empty vessel (tubes) through which water can move easily
Why are xylem vessels rigid?
Because they have thick side walls and rings of hard lignin and so water pressure inside the vessels does not burst or collapse them. The rigid xylem vessels also helps to support the plants
Where is sucrose translocated?
In the sieve tubes of the phloem tissue
Where do plants make sucrose from?
Glucose made by photosynthesis
Describe the process of transpiration
- Water enters roots by osmosis by the root hair cells
- Xylem vessels (due to the cohesive forces holding the water molecules together) draw water up the stem from the roots, lowering its water potential
- Water is drawn out of leaf cells from xylem vessels
- Water evaporates into air spaces in the leaf
- Water vapour diffuses into the air through the stomata
What happens to an air bubble if a fan is started in front of the plant in a transpiration experiment?
The air bubble moves faster because windy days are optimal conditions for transpiration
What happens to an air bubble if the undersides of the leaves are covered with grease?
The air bubble moves slower because the stomatal pores are covered up
Describe the effect of light intensity on the rate of transpiration
Light causes the stomata to open, increasing the rate of evaporation of water from the leaf so more water is taken up to replace this
Describe the effect of air movement on the rate of transpiration
Wind blows moist air away from the stomata, keeping the diffusion gradient high. So the more air movement there is, the higher the transpiration rate
Describe the effect of temperature on the rate of transpiration
The higher the temperature, the more energy water molecules have, so they move faster which means a faster rate of transpiration
How do you use a potometer?
- Note the position of the air bubble on the ruler at the start of the investigation
- Note the position of the air bubble on the ruler after a known number of minutes
- Divide the distance moved by the air bubble by the time taken
How do you calculate the rate of transpiration?
DISTANCE MOVED/TIME TAKEN
Describe the process of translocation
- Transpiration pulls water up the xylem vessels
- Source cells load sucrose into companion cells and the sucrose enter the phloem sieve tubes, reducing water potential
- Water is taken up from the xylem by osmosis, raising the pressure potential in the sieve tube
- Internal pressure differences drive the phloem sap along the sieve tube to sink cells
- Sucrose is unloaded into sink cells, increasing the water potential in the sieve tube
- Water moves back into the xylem by osmosis
Where do the sucrose solution flow through?
The large central channel in each sieve cell connected to its neighbours by holes
What is the tanspiration stream?
A whole column of water and dissolved minerals being pulled upwards from the root to the leaves
What is translocation?
The transport of a sugar through a plant
How does the flow of sucrose act in autumn?
Sucrose moves downwards from the leaves to the roots to be stored as starch
How does the flow of sucrose act in spring?
Sucrose moves upwards from the roots to help the plant grow
What happens when the water flows from the xylem to the sieve tube?
The hydrostatic pressure in the sieve tube increases as the sieve tube’s water potential increases
Where is the sucrose created?
In the source cell
What is water potential?
The concentration of water
How doe sucrose move by?
Active transport
What is water potential?
The concentration of water
What does the phloem do?
Transports dissolved sugars around a plant
What are the 2 separate transport systems in a plant?
Xylem and phloem
Where are dissolved sugars stored to be used later?
Thy are converted to starch and stored in storage organs, e.g. potatoes
Where is sucrose produced?
In leaves from glucose formed during photosynthesis
What is dissolved sucrose needed for?
Growth in growing regions, e.g. the bud
What is the plant tissue responsible for translocation?
Phloem
How can radioactive CO2 be used to show how sucrose is transported from a leaf to a storage organ such as a potato?
- The CO2 is supplied to the leaf and then it is formed into sucrose
- This then is detected in the phloem using a radioactive tracer
- It gets built up into starch in the potato (storage organ)
What cells actively transport the sucrose?
Companion cells
How do mineral ions like nitrate ions enter the root hair?
By active transport
What is active transport?
The net movement of molecules against a concentration gradient from a region of low concentration to high concentration
Why can’t minerals in the root hair not move by diffusion?
The concentration of minerals in the root hair is always very high
Where do mineral ions get energy from to move against a concentration gradient?
Respiration
What does a large surface area mean for root hair cells?
It gives a greater area for osmosis to take place, meaning more water molecules can cross the cell membrane into the cell at the same time
Where is a high concentration of nitrate ions and where is a low?
High - root hair cell
Low - soil
What are the roles of the xylem tissue?
- Carries water and dissolved minerals from the roots to the leaves
- Supports the plant
- Movement in the xylem is always upwards
- Long tubular vessels (xylem vessels) are the main cells found in the xylem; they are dead
What are the roles of the phloem tissue?
- Runs by the side of xylem
- Its tube-like cells carry sucrose up/down the plant
- Unlike xylem, it is living
