**NOT A SUMMARY, THIS IS IN COMPLETE DETAIL**
I attained 99 in Combined Science solely through this self made resource of mine. I have painstakingly gathered information from every EDEXCEL specific resource I could lay my hands on (including seneca, pmt, savemyexams, lit every single video on each...
Edexcel Combined Biology Paper 2:
(Key Concepts is included in Paper 1 bundle)
**NOT A SUMMARY, THIS IS IN COMPLETE DETAIL**
I attained 99 in Combined Science solely through this self made resource of mine. I have
painstakingly gathered information from every EDEXCEL specific resource I could lay my
hands on (including seneca, pmt, savemyexams, lit every single video on each topic i could
find and the EDEXCEL textbook itself) in order to create this incredibly precise document. It
meets every single specification point in meticulous detail, including diagrams and lengthy
explanations where needed. It is the boiling pot of absolutely every single thing you need to
know, nothing more n nothing less, to seize your 99 in GCSE Combined Science.
Key:
- Boldened: Specification point itself
Unit 6: Plant structures and their functions
6.1 Describe photosynthetic organisms as the main producers of food and therefore
biomass
Photosynthetic organisms are plants and algae which are the main producers of food, which
synthesise from sunlight in a process called photosynthesis. They are also therefore the
primary producers of biomass in all food webs and food chains.
6.2 Describe photosynthesis in plants and algae as an endothermic reaction that uses
light energy to react carbon dioxide and water to produce glucose and oxygen
Carbon dioxide + water ----(light)----> glucose + oxygen
6CO2 + 6H2O ---> C6H12O6 + 6O2
> Photosynthesis is an endothermic reaction (takes in more energy than it releases) in which
energy from light is transferred to the chloroplasts in plants.
Plants can use the glucose they make as:
> Source of energy in respiration
> To produce starch for storage
> To synthesise lipids for an energy source in seds
> To form cellulose to make cell walls
> Produce amino acids when combined with nitrogen and other mineral ions to make
proteins
6.3 Explain the effect of temperature, light intensity and carbon dioxide concentration
as limiting factors on the rate of photosynthesis
> Temperature: Increase in temperature means increase in kinetic energy, increasing
likelihood of successful collisions between reactants and enzymes, therefore increased
formation of products so rate of photosynthesis increases. As the reaction is controlled by
enzymes, this trend continues up to a certain temperature until the enzymes begin to
denature and the rate of reaction decreases
> Light intensity: The higher the light intensity, the faster the rate of photosynthesis
> Carbon dioxide concentration: As the concentration of carbon dioxide, the rate of
photosynthesis also increases
> Chlorophyll conc – The more chlorophyll, the more light energy converted, the faster the
,rate of photosynthesis
> Mineral conc: Chlorophyll relies on minerals in order to convert light to energy so more
minerals more healthy working chlorophyll, therefore more light energy converted at once,
the faster the rate of photosynthesis
Any of these factors can be a limiting factor: This is a condition that if is in low levels, it will
restrict any increase in the rate of photosynthesis, despite increases in other factors., the rate
of photosynthesis will not increase anymore (observable when graph levels off)
6.4 Explain the interactions of temperature, light intensity and carbon dioxide
concentration in limiting the rate of photosynthesis
By carrying out an experiment to measure the oxygen production of a plant, the rate of
photosynthesis can be calculated.
> Pondweed is placed in a test tube full of water. The top is sealed with a bung. A capillary
tube also containing water leads into the test tube and is attached to a syringe.
> As it photosynthesises, oxygen is produced, forming a gas bubble in the capillary tube
> The distance the bubble has moved is measured using a ruler to calculate the volume of
oxygen produced in > One variable can be changed (independent variable) at a time to
observe it’s effect on photosynthesis while keeping the others controlled ie The temperature
using a water bath, time the pondweed is left (carbon dioxide conc. effect), light intensity
through a lamp being put at certain intervals to the pond weed.
6.5 Core Practical: Investigate the effect of light intensity on the rate of photosynthesis
Put pondweed in flask with water at room temperature. Cut the tip and seal the flask.
> Use a ruler to place the pondweed flask a certain distance from the lamp ie 15cm
> Leave the apparatus for a certain amount of time to adjust
> Connect the gas syringe to the flask and record the change in volume on the syringe after
5 min
> Move the lamp a certain amount closer ie 5cm closer to be at 10 cm distance and measure
the change in volume again. Repeat.
, Plot results with distance of lamp on x axis and change in gas volume on y axis
In the beginning of the experiment of investigating the effect of light intensity on
photosynthesis rates, a small amount of sodium hydrogen carbonate solution may be added
to the flask with pondweed: This provides excess dissolved carbon dioxide for the plant to
use in photosynthesis, so that it is not a limiting factor.
6.6 Explain how the rate of photosynthesis is directly proportional to light intensity
and inversely proportional to the distance from a light source, including the use of the
inverse square law calculation
Light intensity = (k) rate of photosynthesis so light is directly proportional to the rate of
photosynthesis BECAUSE the greater the light intensity, the more photons hit the
chloroplasts in the leaf, and the more photosynthesis can occur at once.
Therefore:
Light intensity = 1/(distance^2) BECAUSE as the distance between the light source and the
pondweed increases, the light intensity decreases.
6.7 Explain how the structure of the root hair cells is adapted to absorb water and
mineral ions
Root hair cells: These are specialised to take up water by osmosis and mineral ions by active
transport from the soil as they are fount in the tips of roots:
> Have a large surface area due to root hairs, meaning more water can move in
> The large permanent vacuole affects the speed of movement of water from the soil to the
cell
> Mitochondria to provide energy from respiration for the active transport of mineral ions into
the root hair cell
6.8 Explain how the structures of the xylem and phloem are adapted to their function
in the plant, including:
a lignified dead cells in xylem transporting water and minerals through the plant
b living cells in phloem using energy to transport sucrose around the plant
Xylem cells: Specialised to transport water and mineral ions up the plant from the roots to the
shoots
> Upon formation, a chemical called lignin is deposited which causes the cells to die. These
dead cells are said to be ‘lignified’. They become hollow and are joined end-to-end to form a
continuous tube so water and mineral ions can move through.
> Lignin is deposited in spirals which helps the cells withstand the pressure from the
movement of water
Phloem cells: specialised to carry the products of photosynthesis to all parts of the plants
> Cell walls of each cell form structures called sieve plates when they break down, allowing
the movement of substances from cell to cell
> Unlike xylem, these cells within phloem are alive
> Despite losing many sub-cellular structures, the energy these cells need to be alive is
supplied by the mitochondria of the companion cells.
> These cells use this energy to transport sucrose (the sugars plants use) around the plant
6.9 Explain how water and mineral ions are transported through the plant by
transpiration, including the structure and function of the stomata
Transpiration is the loss of water vapour from the leaves and stems of the plant. It is a
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