notes - is234

SECTION 1: Energy in Living Systems
Cells need energy to:
 Move (some bacteria swim)
 Change their shape ( blood cells extend and retract when
engulf invading bacteria cells)
 Manufacture new cellular components
 Maintain and repair cellular structures
 Transport food into the cell
 Expel wastes
All organisms need chemical energy that comes from carbon
compounds in food to carry out their life activities. Almost all of
the energy in carbon compounds comes from the sun. The sun is
the ultimate source of energy for all living things.
Plants, algae, and some prokaryotes carry out Photosynthesis, the
process during which sunlight’s energy is used to change CO₂ and
H₂O into carbon compounds. Organisms that carry out
photosynthesis are called Autotrophs or Producers .
Heterotrophs or Consumers are other organisms , including all
animals and fungi and most bacteria , that cannot perform
photosynthesis and absorb energy by eating other organisms.
The energy stored in food molecules in living cells is gradually
(step-by-step)released in a series of chemical reactions.
Metabolism involves either using energy to build carbon
compounds or breaking down carbon compounds and releasing
energy in them. Metabolism is part of Earth’s carbon cycle.
The main organic compound that cells use is glucose which is
produced during photosynthesis.
6 CO₂ + 6H₂O + energy → Glucose + 6O₂
In order to get energy from glucose organisms use Cellular
Glucose +6 O₂ → 6CO₂ + 6H₂O +
ATP is not very useful for storing large amounts of energy over the
long term. A single sugar molecule stores more than 90 times the
chemical energy. This is why it is efficient for the cells to keep
only small supply of ATP on hand.
Chemical reaction: 6CO₂ +6H₂O+ light →C₆ H₁₂O₆ +6O₂
Inside a Chloroplast:
Molecules that absorb light are called Pigments . The major lightabsorbing pigment in the plants is Chlorophyll which is found in
the chloroplasts of plant cells. Chlorophyll molecules are
contained within disk-like structures called Thylakoids. A stack of
thylakoids is called a Granum. The region outside the thylakoid
membrane in the chloroplast is called Stroma.
Photosynthesis consists of three stages:
Light-dependent reactions(stage 1 and stage 2):
Stage1 – the capture of light energy
The chlorophyll traps the light energy in the electrons
of its atoms
Stage 2- the conversion of light energy into chemical
 Converts ADP to ATP
 Produces oxygen gas
 Takes place within the thylakoid membranes of
ATP synthase is an enzyme that assists in production of
ATP. ATP synthase allows H⁺ ions to pass through the
thylakoid membrane. As the ions pass through, ATP
synthase rotates, binding ADP and phosphate group
together to produce ATP.
Stage 3
Light-independent reaction (Calvin Cycle)(Dark
Reaction) (Carbon fixation)
 Uses CO₂ from the atmosphere
 Uses ATP and NADPH from light-dependent
reaction to produce high-energy sugars
Factors Affecting Photosynthesis
 Availability of water
 Temperature
 Intensity of light
 Carbon dioxide concentration
Concepts you must know:
What are the reactants and the products of photosynthesis?
Name and describe the stages of photosynthesis.
What are the factors affecting the rate of photosynthesis?
Cellular respiration is the process used by humans and most other organisms to release the
energy stored in the food they consume.
Glycolysis –does not require oxygen.(anaerobic)
Takes place in the
 Breaks down glucose
 Produces NADH (electron carrier molecule) from NAD⁺ to be used
 Produces two pyruvate molecules from one glucose molecule.
This stage uses two ATP and makes 4 ATP= net gain of 2 ATP
molecules. 90 % of chemical energy in the glucose is still left.
The Krebs Cycle – aerobic respiration- needs oxygen. Takes place in the
 Pyruvic acid is broken down into carbon dioxide
 Produces 1 ATP molecule for each pyruvate molecule.
Step 3
Electron Transport chain – series of proteins in the inner membrane of
 Uses the electrons from NADH and FADH₂ to convert ADP into
 Produces 34 ATP molecules
62 % of energy in the glucose is not used by cellular respiration and is
released as heat. The waste products of cellular respiration are H₂O and