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A2 Biology
Photosynthesis ­ Unit 4 Section 1
Plants need energy for things like photosynthesis, active transport, DNA
replication, cell division and protein synthesis. Animals need energy for
things like muscle contraction, the maintenance of body temperature, active
transport, DNA replication, cell division and protein synthesis.
Photosynthesis is the process where energy from light is used to break up the
strong bonds in H20; where they Hydrogen molecule is combined with CO2 to
form glucose and O2 is released into the atmosphere. Energy is stored in the
glucose until it is released by places via respiration. Animals obtain their
glucose by eating plants, and respire the glucose as energy. The overall
equation is :
6CO2 + 6H2O = C6H12O6 (glucose) + 602
ATP is the immediate source of energy in cells. This is due to a cell can't
directly get energy from glucose. So in respiration, the energy released from
glucose is used to make ATP; ATP is an made from a nucleotide base adenine,
which is combined with a ribose sugar and three phosphate groups. ATP
carries energy all around the cell to where it is needed. ATP is synthesised
from ADP + Pi this process requires energy from an energy releasing
reaction, such as the breakdown of glucose. The energy is stored as chemical
energy in a phosphate bond. Then the enzyme ATPase comes along and
catalyses the reaction, which breaks the third Phosphate off, releasing energy.
Phosphorylation Adding a phosphate to a molecule E.G ADP is
phosphorylated to ATP
Photophosphorylation Adding phosphate to molecule using light
Photolysis The splitting of a molecule using light energy
Hydrolysis The splitting of a molecule using water
Redox reaction Reactions that involve oxidation and reduction
Some Coenzymes are used in photosynthesis. A coenzyme is something that
aids the function of an enzyme. They work by transferring a chemical group
from one molecule to another.
Photosynthesis takes places in the Chloroplast of plant cells. Chloroplasts are
small, flattened organelles which are found in plant cells. They have double
membranes called a chloroplast envelope. Thylakoid's are stacked up in the
chloroplast into structures called grana. They are all linked together by bits of
thylakoid membrane called Lamellae. Chloroplasts contain photosynthetic
pigments. There are coloured substances that absorb the light energy needed
for photosynthesis. These are found in the Thylakoid membrane. They're
attach to proteins. The pigment and the protein called the photosystem.
There are two which are used by plants, photosystem 1 and photosystem 2.

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Contained in the inner membrane of the chloroplast surrounding the
thylakoid is a gel substance called stroma. It contains enzymes, sugars,
inorganic ions and oil droplets.
There are two stages to photosynthesis, these are the Light Dependant and
light Independent reaction.
The light Dependant Reaction The Light Independent Reaction
It needs light energy This is also called the calvin
It takes places in the Thylakoid cycle.…read more

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Photolysis of water produces protons, electrons and 02 - Photolysis of
water produces protons, electrons and O2, so the electrons move along
the electron transport chain, they must be replaced. Light energy splits
water into proteins electrons and 02
3.…read more

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This reduction reaction also requires H+ ions which come from
the reduced NADP.
Triose phosphate then converts into many useful organic
3. Ribulose phosphate is then regenerated
Five out of every six molecules of TP produced in the cycle are not
used to make hexose sugars, but to regenerate RuBP
Regenerating RuBP uses the rest of the ATP produced by the Light
Dependant reaction.…read more

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Net production: the amount of energy available that is available to the next
trophic level.
Habitat: is the place where an organism lives, such as a stream, tropical
rainforest or a sand dune.
Population: is a group of organisms of the same species, living and breeding
together in a habitat.
Community: is all the populations of the different species of organisms living
together in a habitat at any one time
Ecological niche of an organism is difficult to define.…read more

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Finding a mate: Reproduction is a powerful driving force and the likelihood of
finding a mate.
Territory: many species of animals show clear territorial behaviours.
Parasitism and Disease: they have a devastating effect on individuals.
Every species occupies a different niche. A niche is the role of a species within
a habitat. They have very specific biotic and abiotic interactions which they
need to use. Abundance and distribution of difference species can be
explained by the niche concept.…read more

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There number of
plants and animals in the beginning is much higher.
Happens in the same way but there is already a soil layer so succession
happens at a higher level, so the pioneer plant will be a bigger plant.
At each stage different plants and animals are better adapted as better
abiotic conditions are available. So they move in and out compete the
plants and animals.
As they go on then the ecosystem becomes more complex.…read more

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Can be used to find temperature over thousands of years.
The pollen is preserved in the peat bogs.
Layers accumulate over a long time, so the pollen age increases in
They can take cores from the peat bogs and extract the pollen grains
and identify the plant species in which it came from.
Causes of Global Warming
The scientific consensus is that it is due to human activity.…read more

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Rising temperature
An increase in temperature will affect the metabolism of all organisms.
Normally and increase in the temperature will create the enzyme
reaction to increase, speeding up reactions.
Enzymes have very specific optimum temperatures.
When it increases above this temperature then they decrease the
metabolic reactions.
This means that as metabolic reactions increase then the rate of growth will
increase. But this temperature will increase to much for some organisms, So
there metabolic rates will decrease, meaning there rate of growth will
decrease.…read more

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There are different ways to reduce the increasing CO2 concentrations which
is one cause of global warming. Is to move carbon between organisms and the
atmosphere it called the carbon cycle. The carbon is absorbed by the plants
when they carry out photosynthesis. The carbon is passed to the animals when
they eat the plant, and to the decomposers when the dead organic matter. And
is then returned back to the atmosphere via respiration.…read more


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