2 Organisms in the environment

Question 1

What is the photosynthesis equation?

Answer 1

carbon dioxide + water –>(+light energy) glucose + oxygen

Question 2

How can you show that a plant is photosynthesising?

Answer 2

oxygen is given off as a by-product…
it’s colourless but if you use water plants you can collect the bubbles of gas given off and if they relight with a glowing splint then there is oxygen

Question 3

What is photosynthesis?

Answer 3

the process by which plants (and algae) make food using carbon dioxide, water and light energy

Question 4

What are the parts of the cell in plants and algae which allow photosynthesis to take place? What substance are they filled with?

Answer 4

chloroplasts which contain a (generally green) substance called chlorophyll

Question 5

What happens during photosynthesis?

Answer 5

• light energy is absorbed by the chlorophyll in the chloroplasts
• this energy is then used to convert carbon dioxide from the air plus water from the soil into a simple sugar called glucose
• the chemical reaction also produces oxygen gas as a by-product
• the gas is released into the air, which we can then use to breathe in

Question 6

How is glucose, produced by photosynthesis, used (brief-2)?

Answer 6

• some of the glucose is used immediately by the cells of a plant
• however, a lot of glucose is converted into insoluble starch and stored

Question 7

How can you use iodine to test for starch?

Answer 7

• iodine is a yellowy-brown liquid
• when it reacts with starch, it turns dark blue
• this shows that photosynthesis has taken place in the plant

Question 8

How can you test for starch (explain practical)?

Answer 8

• take a leaf from a plant kept in light and place it in the dark for at least 24 hours
• before iodine is used, leaves must be specially prepared in order for iodine to reach the cells (waterproof cuticle keeps iodine out otherwise and the green chlorophyll would mask any colour changes)
• treat the leaves by boiling them in ethanol first to destroy the waxy outer cuticle and remove the colour
• the leaves are then rinsed in hot water to soften them and then add iodine…

Question 9

How are leaves adapted for photosynthesis?(4)

Answer 9

1 most leaves are broad, giving them a big surface area for light to fall on
2 they contain chlorophyll in the chloroplasts to absorb light energy
3 they have air spaces that allow carbon dioxide to get to the cells and oxygen to leave them by diffusion
4 they have veins, which bring plenty of water to the cells of the leaves
(5 chloroplasts are packed near the surface of the leaf cells in order to absorb the maximum amount of light possible)

Question 10

How are algae also adapted to photosynthesise?

Answer 10

• they are adapted to photosynthesise in the water

- they absorb carbon dioxide dissolved in the water around them

Question 11

What are limiting factors?

Answer 11

a factor which limits the rate of a reaction e.g. temperature, pH, light levels (photosynthesis)

Question 12

How might the rate of photosynthesis be limited?

Answer 12

• shortage of light
• low temperature
• shortage of carbon dioxide

Question 13

Explain what happens when light is a limiting factor of photosynthesis:

Answer 13

• if there is plenty of light then lots of photosynthesis can take place…
• …if there is very little or no light then photosynthesis will stop
• it will remain stopped no matter what conditions there are around the plant
• for most plants… “the brighter the light, the faster the rate of photosynthesis”
• when the line on the graph remains at a constant rate of reaction it means that light is no longer the limiting factor

Question 14

Explain what happens when temperature is a limiting factor of photosynthesis:

Answer 14

• affects all chemical reactions
• as the temperature rises, the rate of photosynthesis increases because the reaction speeds up
• however, photosynthesis is controlled by enzymes…
• …most enzymes are destroyed/denatured once the temperature has risen to around 40-50 degrees C so if the temperature is too high then the rate of photosynthesis will fall because the enzymes controlling photosynthesis are denatured

Question 15

Explain what happens when carbon dioxide is a limiting factor of photosynthesis:

Answer 15

• plants need CO2 to make glucose
• the atmosphere only contains about 0.04% CO2…
• …this means that often these levels limit the rate of photosynthesis
• increasing carbon dioxide levels increases the rate of photosynthesis
• on a sunny day, carbon dioxide levels are the most common limiting factor for plants because…
• …levels rise at night due to respiration and no photosynthesis but then as light and temperature levels increase in the morning, the carbon dioxide gets all used up

Question 16

How can we decrease limiting factors in photosynthesis?

Answer 16

• in a science lab or greenhouse we can manage the levels of light, temperature and carbon dioxide artificially meaning they are no longer limiting
• this means the rate of photosynthesis can increase
• in a garden or woodland these factors are harder to pinpoint and control

Question 17

How do plants and algal cells use the soluble glucose they produce using photosynthesis?

Answer 17

• for respiration
• to convert into insoluble starch for storage
• to produce fats or oils for storage
• to produce fats, proteins or cellulose for use in the cells and cell walls

Question 18

How do plants respire?

Answer 18

• the glucose, produced by photosynthesis, is broken down using oxygen
• this provides energy for the cells
• CO2 and water are the waste products for the reaction

Question 19

How (and why) do plants and algal cells make amino acids?

Answer 19

• plants use some of the glucose from photosynthesis and combine sugars with nitrate ions and other mineral ions from the soil
• these amino acids are then built up into proteins to be used in cells
• this uses energy from respiration
• alga also make them but take nitrate ions and other materials they need from the water around them

Question 20

Why are fats and oils built up using energy from respiration and glucose from photosynthesis?

Answer 20

• to be used in cells as an energy store
• to be used by cell walls to make them stronger
• to be used as an energy store in their seeds, providing lots of energy for the new plant as it germinates

Question 21

How is food moved throughout the plant?

Answer 21

by the pholem

Question 22

Why do plants convert glucose into starch to be stored?

Answer 22

• glucose is soluble in water…
• …this means if it was stored in plant cells it could affect the way the water moved in and out of the cells and affect the water balance of the whole plant
• starch is insoluble in water…
• …it will have no effect on the water balance of the plant which means it can be stored in large amounts

Question 23

Even though starch is present throughout a plant, why do plants keep insoluble starch in special storage areas?

Answer 23

• to produce tubers and bulbs
• these help them survive the winter when they can’t photosynthesis
• they are filled with starch (we often eat them ourselves e.g.potatoes and onions)

Question 24

Why do we use greenhouses (polytunnels)?

Answer 24

• to control limiting factors with artificial influence such as more light, a perfect temperature and higher levels of CO2
• to increase the rate of photosynthesis…
• …this means the plants grow faster, flowering and producing fruit earlier with a larger yield
• it also means we can grow any food in the preferred conditions
• although building the greenhouses are a lot of money, the turnover is fast with high profits, the crops are clean and unspoilt, there is no ploughing or preparation of the land required meaning crops can be grown where land is poor

Question 25

How else, other than controlling limiting factors, can plants be grown better?

Answer 25

• in water with a perfect balance of mineral ions instead of soil, so nothing slows their growth
• technology known as hydroponics

Question 26

What are the physical factors which affect living organisms in their environment?

Answer 26

• temperature
• nutrients
• the amount of light
• the availability of water
• the availability of oxygen and carbon dioxide

Question 27

How does temperature affect living organisms in their environment?

Answer 27

• cold climates = temperature is always a limiting factor
• less photosynthesis for plants mean they are small and this in turn affects the numbers of herbivores which can survive in the area (meaning they will have to continuously migrate)

Question 28

How do nutrients affect living organisms in their environment?

Answer 28

• the level of mineral (nitrate) ions has a big impact on the distribution of plants
• carnivorous plants such as venus fly traps thrive where nitrate levels are low because they can trap and digest animal prey (the nitrates they need are provided when they break down the animal protein)
• most other plants struggle to grow in areas of mineral ion deficiency

Question 29

How does the amount of light affect living organisms in their environment?

Answer 29

• light limits photosynthesis which affects the distribution of plants and animals
• some plants are adapted to living in low light levels meaning they may have more chlorophyll or bigger leaves (however most need plenty of light to grow well)
• the breeding cycles of many animal and plant species are linked to day length-they only live and breed in regions where day length and light intensity are right for them

Question 30

How does the availability of water affect living organisms in their environment?

Answer 30

• very important, especially in deserts
• in deserts, plants and animals are relatively rare
• the distribution changes after it rains…a large number of plants grow, flower and set seeds very quickly whilst water is available
• these plants are eaten by many animals that move into the area to take advantage of them
• if there is no water, there will be little or no life

Question 31

How does the availability of oxygen and carbon dioxide affect living organisms in their environment?

Answer 31

• big impact on water-living organisms
• some invertebrates can survive in water with very low oxygen levels however most fish need a high level of dissolved oxygen
• the distribution of land organisms is not affected by oxygen levels because generally there is plant of oxygen in the air and levels vary very little (unless traveling to high altitudes)
• CO2 levels act as a limiting factor on photosynthesis
• it can also affect the distribution of organisms e.g.mosquitoes are attracted to animal’s blood by high CO2 levels
• plants are also vulnerable to insect attacks in an area with high CO2 levels

Question 32

How can you get quantitative data on the distribution of organisms in the environment?

Answer 32

by using:

• random sampling with quadrats (square frame)
• sampling along a transect (not random, equal interval spacing)

Question 33

Why is sample size important?

Answer 33

• to get accurate results

- to get valid results

Question 34

Why is it good to take random samples?

Answer 34

• ensures your results reflect the true distribution of organisms
• any findings you make will be valid

Question 35

What is quantitative sampling and how can you use it?

Answer 35

• taking a number of random readings and then finding the mean number of organisms
• can use it to compare the distribution of the same organism in different habitats and to compare the variety of organisms in different habitats

Question 36

How is a line transect useful?

Answer 36

• can sample at regular intervals
• can show how the distribution of organisms changes along the line
• can also measure some physical factors such as light levels and soil pH which might affect or explain your results

Question 37

What are the 4 main types of average?

Answer 37

• mean
• median
• mode
• range

Question 38

What is a reproducible investigation?

Answer 38

one which can be repeated by other people to get very similar or the same results

Question 39

What is a valid investigation?

Answer 39

must be able to answer the question/hypothesis

Question 40

Why must the validity and reproducibility of an investigation be considered carefully?

Answer 40

it is difficult to control variables in field work

sample size is also an important factor