1. B4 Bioenergetics Photosynthesis Plant use glucose for:
The following equations summarise what happens in photosynthesis:
Photosynthesis is the process by which plants make carbohydrates
from raw materials, using energy from light. During photosynthesis:
light energy is absorbed by chlorophyll - a green substance found in chloroplasts in green plant cells and algae
absorbed light energy is used to convert carbon dioxide (from the air) and water (from the soil) into a sugar called glucose
oxygen is released as a by-product
Plant use glucose for:
Making amino acids
Glucose is combined
with nitrate ions
( from the soil) to make
amino acids, they are used
to make up proteins
Making cellulose
Cellulose is present in cell walls, it strengthens cell walls
Respiration
Energy from respiration is use to convert rest of the glucose in to useful substances , build new cells and grow
Storage of lipids and starch
Plants can convert glucose in to lipids and store them in seeds
Pants can convert glucose in to starch and store it in roots, stems, seeds and leaves
B4 Bioenergetics
temperature
If it gets too cold, the rate of photosynthesis
will decrease. Plants cannot photosynthesise
if it gets too hot.
light intensity
Without enough light, a plant cannot photosynthesize
very quickly - even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the rate of photosynthesis.
Enzymes increase rate of process,
Their action depends from temperature
rate increase with temperature
To high (above 45 C) enzyme will be damaged
carbon dioxide
concentration
The amount of CO2
will increase rate of
process up to a point,
after that point
rate no longer
increase
As the light level is raised, rate of photosynthesis
increase up to the point No increase after that point
Factors affecting
photosynthesis
Three factors can limit the rate
of photosynthesis:
Even if there is plenty of light, a plant cannot photosynthesise
if there is insufficient carbon dioxide

2. B4 Bioenergetics Metabolism
Photosynthesis limiting factors: temperature, carbon dioxide, light
HT: at any given time, any one of these factors
may be limiting the rate of photosynthesis. This
can be shown on graphs – see example. When it
comes to light intensity, it varies with distance
according to an inverse square law:
In commercial growing of plants (e.g. tomatoes
in a greenhouse), the conditions are optimised
to maximise the rate of photosynthesis and
obtain the highest profit.
Chemical reactions are controlled by enzymes
Metabolism
Metabolic pathways can be described
as a series of chemical reactions that start with a substrate and finish with an end product.
The sum of ALL the chemical reactions happening in a cell or in the whole body. 1
Light intensity =
distance (d) 2
Endothermic reactions
– larger molecules are
made up from smaller ones , reaction take in energy from environment
Exotermic reactions:
Larger molecules are broken down into smaller ones,
energy is transferred in to the environment
B4 Bioenergetics
Making lipid (fat) molecules from one molecule of glycerol and three molecules of fatty acids
Heat from the
sun
Conversion of glucose:
to glycogen (in animals),
to starch or cellulose (in plants).
Breaking down excess
proteins into amino acids, then into urea for excretion in the urine.
Artificial light
t after Sun
CO2 concentration
- Use of paraffin heater,
Investigating photosynthesis rate
In plants, glucose is combined
with nitrate ions to make amino acids. These amino acids are then used to synthesise proteins.
Glucose is broken down
In Respiration, energy is
used to power all reactions in the body
Use a pondweed to investigate the effect of different
light intensity on the rate of photosynthesis- the
faster the rate of oxygen produced by pondweed, the
faster the rate of reaction.
cellulose
Controlling variables:
Independent variables
– light intensity
Dependent variable
– amount of oxygen produced

3. Anaerobic respiration
Aerobic respiration occurs when
oxygen is used in the reaction.
Anaerobic respiration happens
inside the cell structures called
mitochondria.
Respiration.
Respiration is a process of transferring energy from glucose,
which goes on in every cell. All animals and plants respire, it’s
how they release energy from their food. All reactions involved in respiration are catalysed by enzymes, respiration is exotermic – it transfers energy to the environment. There are two types of respiration aerobic and anaerobic.
word equation:
glucose + oxygen  carbon dioxide + water
Symbol equation:
C6H12 O6 + 6O6  6CO6 + 6H2O
Living organism , use released energy for their life processes.
• Chemical reactions to build larger
molecules from smaller ones.
E.g. making proteins such
as enzymes from amino acids.
• Keeping warm. This is an example of
homeostasis: using energy from respiration
to maintain body temperature at a set point (37 ֩C).
• Movement. E.g. movements of
our body are possible due to muscle contractions. This requires energy from respiration.
Aerobic respiration
Anaerobic respiration
Is oxygen needed?
yes no
What products are made?
CO2 and water
Lactic acid (muscles), CO2, ethanol (plants, yeast)
How much energy is transferred?
Large amount
Most efficient
A small amount
Plants and yeast:
Word equation:
glucose  ethanol + carbon dioxide
Symbol equation:
C6H12O6  2C2H5OH + 2CO2
Anaerobic respiration
Anaerobic respiration occurs
when there is insufficient
oxygen available for
complete breakdown of the
glucose.
The reaction that happens is
different in animal cells compared to plant and yeast cells.
Energy for exercise
During exercise, more energy is required as muscle contract more frequently. This energy comes from increased respiration. Increased respiration in cells means that more oxygen is needed. Therefore physical activity:
During exercise when body can’t supply oxygen to muscles, they start to respire anaerobically.
Lactic acid builds up
and exercise can
cause muscle fatigue.
Fermentation
- we call the anaerobic respiration in yeast. This is a very useful process:
for making bread; the CO2 makes it rise
making alcoholic drinks, beer and wine;
ethanol type of alcohol is produced.
Increases heart rate to
make blood flow in faster rate, delivering more oxygen and glucose to cells, and taking carbon dioxide away
Animals
Word equation in muscles:
glucose  lactic acid
Oxygen debt
Is amount of extra oxygen the body
need after exercise to react with build up lactic acid and remove it from the cells.
Increases breathing
rate and volume of each
breath to meet demand for oxygen