Photosynthesis Flashcards Preview

IGCSE Biology Part 2- Plant biology and ecology > Photosynthesis > Flashcards

Flashcards in Photosynthesis Deck (82):

what is photosynthesis?

the process by which green plants and some other organisms convert light energy from the sun into chemical energy


what is the word equation for photosynthesis?

carbon dioxide + water (in presence of chlorophyll and light) = glucose + oxygen


what is the balanced symbol equation for photosynthesis?

6CO2 + 6H20 = C6H1206 + 6O2


describe the process of photosynthesis?

light energy is absorbed by chlorophyll, light is then used to convert carbon dioxide and water into glucose. Oxygen is a byproduct of this process.


how is energy conserved in plants?

the chemical energy created from the light is converted into glucose. This energy is passed down the food chain, as animals consume plants. This is why plants are referred to as "producers" of the food chain as they make their own food.


how do you test a leaf for starch?

1. heat a plant leaf in boiling water for 30 seconds (this stops its chemical reactions)
2. heat it in boiling ethanol for a few minutes (this removes most of its colour)
3. wash with water and spread onto a white tile
4. add iodine solution from a dropping pipette
5. after a few minutes, the bits containing starch will turn blue/black


describe an experiment to show chlorophyll is needed for photosynthesis

1. use a variegated (green and white) leaf (only green plants contain chlorophyll)
2. take the variegated leaf from a plant that has been exposed to light
3. record which parts are green and which aren't
4. test the leaf for starch; only the green bits will turn blue/black


describe an experiment to show carbon dioxide is needed for photosynthesis

1. put a plant inside a sealed (bell) jar, keeping factors constant e.g. light, temperature etc.
2. use soda lime to absorb CO2 out of the air in the jar
3. leave the plant in the jar for a while before testing it for starch
4.the leaf shouldn't turn blue/black as CO2 is required for photosynthesis


how are leaves adapted for photosynthesis?

- large surface area to absorb more light
- thin- short distance for carbon dioxide to diffuse into leaf cells
- chlorophyll- absorbs sunlight to transfer energy into chemicals
- network of veins- to support the leaf and transport water and carbohydrates
- stomata- allow carbon dioxide to diffuse into the leaf


label the inside of a leaf


what is the purpose of the epidermis and how is it adapted?

it is thin and transparent to allow more light to reach the palisade cells


what is the purpose of the wax cuticle?

to protect the leaf without blocking out light


what is the purpose of the palisade layer at the top of a leaf?

contains chloroplasts to absorb more light


what is the purpose of the spongey mesophyll layer?

air spaces allow carbon dioxide to diffuse through the leaf, and increase the surface area


what is the purpose of palisade cells?

they contain many chloroplasts to absorb all available light


what is the function of guard cells?

they help to regulate the rate of transpiration by opening and closing the stomata. They facilitate gas exchange for photosynthesis and help minimise water loss.


how is the structure of the leaf adapted for gas exchange?

- leaves have a large surface area for diffusion
- cells in the spongey mesophyll are loosely packed and covered by a film of water, letting gases move easily between cells
- thin- gases only need to travel a short distance to reach needed cells
- contain stomata at lower surface letting gases diffuse in and out
- stomata closes when it gets dark controlled by guard cells as it doesn't need to let CO2 in as plants can't photosynthesise in the dark


describe an experiment using oxygen production to show the rate of photosynthesis (light intensity)?

use pondweed to see how light intensity affects the rate of photosynthesis:
- put a lamp next to a beaker filled with water and pondweed in
- put the lamp 10cm away from the beaker
- leave for 5 mins for the pondweed to acclimatise to the new light intensity
- count the number of bubbles given off in one minute
- move the light 10cm further back
- leave for 5mins for pondweed to acclimatise again
- count bubbles for 1 minute
- repeat by moving lamp away by 10cm intervals until reaching 50cm


how does carbon dioxide concentration affect the rate of photosynthesis?

a plant cannot photosynthesise without carbon dioxide therefore an increase in co2 concentration results in an increase in photosynthesis rates. However this happens only until a certain point as if you keep increasing co2 levels you will have to increase water and sunlight rates too to allow it to keep increasing


how does light intensity effect the rate of photosynthesis?

without enough light, a plant cannot photosynthesise very quickly so if light intensity is increased then the rate of photosynthesis increases. However this only happens up to a certain point as there would also have to be plenty of water and co2 present.


how does temperature effect the rate of photosynthesis?

if the plant is at optimum temperature, its rate of photosynthesis will be the highest as enzymes will work at their best. If the temperature is too high, the plant could burn or its enzymes will denature, bringing down the rate of photosynthesis but until that point, the higher the temperature, the higher the rate of photosynthesis as it has more energy from heat. If it gets too cold, the rate of photosynthesis will decrease.


what is diffusion?

the movement of particles from an area of high concentration to an area of low concentration


what is the role of diffusion in gas exchange in a leaf?

oxygen and evaporated water diffuse out of the leaf into the air (via the stomata) and carbon dioxide diffuses into the leaf. The concentration of the oxygen, carbon dioxide and water vapour in the leaf are different to allow diffusion to take place


what is the symbol equation for respiration?



what happens in the gas exchange in photosynthesis?

the plant takes up carbon dioxide and gives out oxygen


what happens in the gas exchange in respiration?

the plant gives out carbon dioxide and uses oxygen


why does net exchange of carbon dioxide and oxygen depend on light intensity?

during the day the net exchange of carbon dioxide and oxygen is balanced as both respiration and photosynthesis are occurring. Oxygen and carbon dioxide are both being used and produced. During the night only respiration will occur so oxygen will be used and co2 will be produced so the net exchange of oxygen will have an increased input and the net exchange of carbon dioxide will have an increased output as photosynthesis will not be occurring


when does respiration occur?

respiration takes place all the time so oxygen will be taken in by respiring cells, and carbon dioxide will be produced as a waste product as oxygen is always present in the air


when does photosynthesis occur?

photo synthesis only occurs during the day as it depends on light which is not present during night time


describe an experiment to investigate the effect of light on net gas exchange of a leaf

- take 4 test tubes and add the same volume of hydrogen-carbonate indicator to each test tube
- collect three similar sized leaves and place them in the indicator
- place aluminium round one leaf, baking paper around another and nothing around one
- check the colour of the indicator (normal co2 levels= red, increased/high co2 levels= yellow, decreased/low co2 levels= purple)
- repeat for a reliable experiment
- the 4th test tube in the experiment is a control test. If the indicator in the test tube changes colour, there is something wrong with the experiment


what is the role of stomata in gas exchange?

the stomata control gas exchange in the leaf. Each stoma can be open or closed, depending on how turgid its guard cells are


what are stomata?

tiny pores in the surface of the leaf, most of these are in the lower epidermis, away from the brightest sunlight


what do guard cells do?

guard cells regulate the opening and closing of the stomata; allowing carbon dioxide and oxygen to be exchanged between the leaf and the atmosphere


how is oxygen lost from the stomata of a leaf?

oxygen is one of the waste products of photosynthesis and leaves the leaf through the stomata


how is carbon dioxide lost from the stomata of a leaf?

carbon dioxide is a waste product of respiration and is excreted from the leaf through the stomata


why are there more stomata on the lower surface of a leaf than on the upper surface?

the upper surface is more exposed to sunlight and this may cause the leaf to lose too much water by evaporation or lose it too quickly


what happens when guard cells are turgid?

when they are turgid they expand, bend outwards and open the stoma (high water)


what happens when the guard cells are flaccid?

when they are flaccid they bend inwards and close the stoma (low water)


how do plants absorb minerals?

they are absorbed through the roots as mineral ions dissolve in the soil water


why do plants require nitrates?

used for making amino acids, which are used to make proteins


why do plants require magnesium?

for making chlorophyll


what will happen if a plant is deficient in nitrate?

it will suffer from stunted growth


what will happen if a plant is deficient in magnesium?

its leaves will turn yellow


why do plants require mineral ions?

for healthy growth


how is water absorbed by root hair cells?

they absorb minerals by active transport and water by osmosis


what are root hairs?

root hairs are epidermal cells on the surface of the root


what is the function of root hairs?

to collect water and mineral nutrients present in the soil


how are root hairs adapted for their function?

- they have a large surface area for absorption and to speed up osmosis
- they branch to increase the surface area and increase the chances of finding a water source


how does xylem transport water to other parts of the plant?

- water is absorbed from the soil through root hair cells
- water moves by osmosis from root cell to root cell until it reaches the xylem
- it is transported through the xylem vessels up the stem to the leaves
- it evaporates from the leaves (transpiration)


what are xylem tubes made from?

dead xylem cells which have the cell walls removed at the end of the cells, forming tubes through which the water and dissolved mineral ions can flow. The rest of the xylem cell has a thick, reinforced cell wall which provides strength


what is the role of phloem?

phloem vessels are involved in translocation. Dissolved sugars, produced during photosynthesis, and other soluble food molecules are moved from the leaves to growing tissues and storage tissues


how is phloem structured?

phloem consists of columns of living cells. The cell walls of these cells do not completely break down, but instead form small holes at the end of the cell. The ends of the cell are referred to as sieve plates. The connection of phloem cells effectively forms a tube which allows dissolved sugars to be transported


how is water transported into the roots of plants?

- the water in the soil is a weaker solution than that of the root hair
- therefore water enters the root by osmosis
- this makes the solution in the cell weaker and then water can then move into the next cell by osmosis
- this continues until water moves into the xylem
- pressure difference caused by water loss in the leaf then pulls the water up to the leaf


what is transpiration?

the loss of water from a plant


explain transpiration in a leaf.

water on the surface of spongy and palisade cells evaporates and then diffuses out the leaf. More water is drawn out of the xylem cells inside the leaf to replace what's lost. The xylem cells make a continuous tube from the leaf, down the stem to the roots, this acts like a drinking straw, producing a flow of water and dissolved minerals from roots to leaves.


what factors affect the rate of transpiration?

- light
- temperature
- wind
- humidity


how does light affect the rate of transpiration in plants?

an increase in light intensity results in an increase in transpiration due to an increased stomata opening. Evaporation of water occurs primarily through the stomata so more water is lost


how does temperature affect the rate of transpiration in plants?

transpiration is faster in higher temperatures. Evaporation and diffusion are faster at higher temperatures


how does wind affect the rate of transpiration in plants?

transpiration is faster in windy conditions. Water vapour is removed quickly by air movement, speeding up diffusion of more water vapour out of the leaf


how does humidity affect the rate of transpiration in plants?

transpiration is slower in humid conditions. Diffusion of water vapour out of the leaf slows down if the leaf is already surrounded by moist air


describe an investigation to investigate the role of environmental factors in determining the rate of transpiration.

- cut a shoot underwater at a slant (to prevent air from entering the xylem)
- set a potometer up underwater (to prevent the formation of air bubbles)
- remove the apparatus from the water, but keep the end of the capillary tube inside a beaker of water
- check that the apparatus is watertight and airtight, then dry the leaves
- remove the capillary tube from the water, until an air bubble forms, then put it back
- record the starting position of the air bubbles
- use a stopwatch to record how far the bubble moves in a certain time. Faster the bubble moves faster rate of transpiration


using the potometer experiment, how can you measure how each environmental factor affects transpiration?

- light intensity- cupboard/ lamp
- temperature (warmer/colder room)
- humidity- spray bit of water into clear plastic bag before sealing round plant
- wind speed- fan


what is phototropism?

when a plant responds to light


what is a tropism?

a growth in response to a stimulus


what happens when plants respond to a stimulus?

plant shoot tips (called coleoptiles) produce the hormone auxin, which controls the direction of growth; causing them to grow towards the light. Because the plant is growing towards the light, we call it positive phototropism


what is positive phototropism?

when the plant grows towards the stimulus


what is negative phototropism?

when the plant grows away from the stimulus


what is gravitropism (geotropism)?

a tropism where gravity is the stimulus


how do auxins make plants grow towards the light?

in phototropism the cells on the plant that are farthest from the light have more auxin diffuse from the coleoptiles. The auxin causes the plant to have elongated cells on the farthest side from the light. Therefore the plant bends towards the light.


what is the geotropic response of roots?

roots are positively geotropic:
- when roots grow sideways, more auxin is produced on its lower side
- in roots, extra auxin inhibits growth, so the cells on the top elongate faster, causing the root to bend downwards


what is the geotropic response of shoots?

shoots are negatively geotropic:
- when shoots grow sideways, gravity produces unequal amounts of auxin at the tip, with more auxin on the lower side
- this causes the lower side to grow faster, and so the shoot bends upwards


what is auxin?

a plant hormone which causes the elongation of cells in shoots and is involved in regulating plant growth.


what is osmosis?

the movement of water from a less concentrated solution to a more concentrated solution through a partially permeable membrane


what is found in a plant cell?

- nucleus
- cytoplasm
- cell membrane
- mitochondria
- ribosomes
- cell wall
- chloroplasts
- permanent vacuole


what is the function of the nucleus?

controls genetic material, which controls the activities of the cell


what is the function of cytoplasm?

most chemical processes take place here, controlled by enzymes


what is the function of the cell membrane?

controls the movement of substances into and out of the cell


what is the function of mitochondria?

most energy is released by respiration here


what is the function of ribosomes?

protein synthesis happens here


what is the function of the cell wall?

strengthens the cell


what is the function of chloroplasts?

contain chlorophyll, which absorbs light energy for photosynthesis


what is the function of the vacuole?

filled with cell sap to help keep the cell turgid