Biology - B2.2 - Organisms In the Environment - Revision Cards in GCSE Biology

B2.2.1 - Photosynthesis

Photosynthesis can only be carried out by green plants and algae
Chlorophyll in the chloroplasts absorbs the Sun's light energy
Carbon dioxide + water ->light energy-> glucose + oxygen
Process for photosynthesis - CO2 taken in by leaves and H2O taken in by roots -> chlorophyll traps light energy -> energy is used to convert the CO2 and H2O to glucose
Oxygen - by-product
Some glucose changed into insoluble starch for storage
Testing leaves with iodine solution - identify starch in leaf and show photosynthesis occured - variegated leaves have green (with chlorophyll) patches and white (without chlorophyll) patches - only green patches turn iodine blue/black - presence of starch

1 of 7

Lack of light - slow down photosynthesis as light provides energy for process - sunny days, plants may be limited by shade
Cold - enzymes don't work effectively - slow down photosynthesis
Lack of CO2 - slow down photosynthesis - limited in a closed space eg. greenhouse - sunny day - plenty of light, not enough CO2
Anything stopping photosynthesis = limiting factor
When doing photosynthesis experiments - limiting factors must be controlled - variables to be controlled: light, temperature and type of plant

2 of 7

Uses of soluable glucose - glucose produced by photosynthesis may be:
- converted to insluble starch for storage
- used for respiration
- converted to fats and oils for storage
- used to produce cellulose - strengthens cell walls
- used to produce proteins
Plant and algae cells - also need supply of mineral ions - eg. nitrate ions - to produce protein - absorb nitrate ions from soil or water they live in

3 of 7

Plant growers ontrol environment - give plants best growing conditions - have to evaluate benefits of increading growth with increased cost of heating, lighting or producing CO2
Greenhouses and polytunnels - constructed to grow plants in enclosed space - may have heaters and lamps to increase photosynthesis, but may stop if too hot or too much bright
CO2 added to the air to increase photosynthesis
Nitrate ions added to soil so plants can make proteins needed for growth
Expensive to produce suitable temperature, light and CO2 - must compare biomass of plants grown inside and outside without extra factors

4 of 7

Living organisms form communities - relationships between and within communities - can be influenced by external factors
Physical factors affecting distribution of organims:
- Temperature - small plants = limited number of plant eaters
- Nutrients - short supply of mineral ions = less plants = less animals
- Light - few plants live on forest floor - shade - shaded plants have broader leaves or more chlorophyll
- Water - desert - when it rains, plants grow, flower and seed quickly - food for animals
- Oxygen - water animals affected by low oxygen - some invertabrates can live at low oxygen levels but most fish need high levels
- CO2 - low CO2 will affect plant growth = less animal food

5 of 7

Quantative data - used to describe affect of physical factors on distribution of organisms in a particular habitat - obtained by: random quantative sampling using a quadrat or sampling along a transect
Qudrat - square frame - may be subdivided into a grid - several quadrats placed randomly in a field, investigator counts number of a particular plant or animal - used to estimate no of (eg.) daisies in a field
Sample size - enough quadrats placed to be representative of entire area
An estimate is usually given by x mean/sq m
Transect - not random - line marked between two points -> quadrat placed at regular intervals down line -> organisms counted - physical factors could also be measured at each point - supplies lots of information about habitat and organisms in it

6 of 7

Difficult to experiment on distribution of organisms - done over long period of time - uncontrollable variables
Transect made - comparative investigation must be done at same time of day - control variable
Valid investigation - all possible variables must be controlled
Repeatable - same experimenter does same thing with same equipment and gets same results - may make mistake both times
Reproducible - different person or different equipment and techniques are used and get same results
Sample size - needed for valid, repeatable and reproducible results - too small = not representative - larger sample size = more trusted data

7 of 7