2. is reduced, less thermal energy is lost to the environment)
● Shivering, which generates body heat
● Makes us aware of the low temperature
●
1.2. Cell Structure
1.1.1 General information
● Parts of a cell: chloroplasts, cell membrane, cell wall, cytoplasm,cell vacuoles, nucleus,
mitochondria, ribosome, smooth and rough endoplasmic reticulum, golgi apparatus,
lysosome and cilia
● Prokaryotic cells are probably not tested.
● Eukaryotic cells have membranebound organelles and a true nucleus is present.
● Diagram
1.1.2. Functions and
structure
● Cell wall
→ Usually found in plant and
bacteria cells
→ consists of cellulose fibres
(carbohydrates)
→ provides structural support
to the cell and the plant due to
its mechanical strength
● Nucleus
→ contains chromatin which
controls cell activities
8. 1.3 Transport in Cells
1.3.1. Passive Transport
● no energy is required to move a substance (such as water or carbon dioxide)
● from an area of high concentration to an area of low concentration until the concentration
is equal, sometimes across a membrane.
● The hightolow concentration gradient is the driving force for passive transport because
it fulfills a fundamental law of nature: Things tend to move from a highenergy, ordered
structure to a lowerenergy, increasing randomness, or increasing entropy state of being.
Diffusion
● Certain molecules, such as oxygen, simply move directly through a membrane in
response to the hightolow concentration gradient. As an example, oxygen diffuses out
of the lungs and into the blood for transport to all of the cells.
Facilitated Diffusion
● Substances are sometimes too large to move freely through a membrane, or they need
to move against a concentration gradient so transport proteins embedded in the
membrane assist with the passage.
● Transport protein creates a chemical channel for the passage of a specific substance.
Because no energy is expended, the rate of facilitated diffusion depends on the number
of transport proteins embedded in the membrane.
● e.g. Glucose is moved by a glucosetransporter protein as it passes through the red
blood cell into a body cell.
Osmosis
● similar to diffusion
● refers only to water diffusing through a permeable membrane.
● Water as a solvent moves from an area of high to low concentration.
● water flows from a lowsolute to a highsolute concentration until the concentration is
equal.
● The solution that has a highsolute concentration is a hypotonic solution relative to
another lowersolute concentration or hypertonic solution.
● Water will continue to osmotically move from the lowsolute/highsolvent concentration
toward the highsolute/lowsolvent concentration until both sides are isotonic, or equal.
Ion channels.
Protein channels
● These are membrane proteins that allow the passage of ions that would ordinarily be
stopped by the lipid bilayer of the membrane.
● These small passageways are specific for one type of ion, such that a calcium ion could
not pass through an iron ion channel.
● The ion channels also serve as gates because they regulate ion flow in response to two
environmental factors: chemical or electrical signals from the cells and membrane
movement.
Active Transport
● Sometimes substances must be pumped against a concentration gradient, such as the
9. sodium ions (Na+) and potassium ions (K+) pump.
● So a transport protein and energy, usually adenosine triphosphate (ATP), the energyrich
compound, are needed to push the ions against the gradient.
● In the case of sodium and potassium ions, maintaining sodium outside and potassium
inside the cell is crucial to the functioning of muscles and nerves.
● The following mechanism illustrates an active transport mechanism:
1. Sodium ions inside the cell bind to the transport protein as a phosphate is added from an ATP,
which changes the shape of the transport protein.
2. The new transport protein structure carries and deposits the sodium to the exterior and bonds
with a potassium ion, loses the phosphate group (which again changes the shape of the
transport protein), and allows for the return trip.
3. The potassium is deposited inside the cell, and a sodium ion and a phosphate are attached to
a transport protein to repeat the process.
Endocytosis and exocytosis
● for big molecules, such as long protein chains or ringed structures, as well as the bulk
volume of small molecules.
● In endocytosis, substances such as food are brought into the cell in a process in which
the cell membrane surrounds the particle and moves the particle inside the cell, creating
a vacuole or vesicle as a membraneenclosed container. I
● n exocytosis, waste products or hormones, which are contained in vacuoles or vesicles,
exit the cell and their containing membrane is absorbed and added to the cell membrane.
● There are three types of endocytosis:
→ Pinocytosis occurs when the cell absorbs fluid from the exterior, creating a fluid vacuole.
→ Receptormediated endocytosis is a special type of pinocytosis that is activated by the
identification of a receptor protein sensitive to the specific substance.
→ Phagocytosis is the engulfing and digesting of substances, usually food, by vacuoles with a
lysosome attached (a lysosome is an organelle that contains digestive enzymes).
2. Biomolecules
2.1. Carbohydrates
● Contain the elements C, H, O
● They are either made from single monosaccharide monomers or from several
monosaccharides joined together
● general formula (CH2O)n
2.1.1. Monosaccharides
● Monosaccharides are:
→ Trioses – C3H6O3 (e.g. glyceraldehyde)
→ Pentoses – C5H10O5 (e.g. deoxyribose)
→ Hexoses – C6H12O6 (e.g. glucose, fructose)
12. 2.2. Water
2.2.1 Properties of water
● high heat capacity
● high heat of vapourisation
● high heat of fusion
● most dense at 0 degrees Celsius
● density of water decreases as the temperature increases when the temperature is above
0 degrees Celsius
● density of water decreases as the temperature of water decreases from 4 degrees to 0
degrees
● water has high cohesion (force of attraction between like molecules) due to hydrogen
bonds
● an effect of high cohesion is high surface tension
● In clear water, red and yellow light can reach a depth of 50 metres while blue and violet
light can penetrate 200metres deep.
● The ability of light to penetrate water enables photosynthetic organisms to occupy the
vast volumes of lakes and oceans
● water has low viscosity
2.2.1.1. Water as a solvent
● many substances are dissolved in the water of biological fluids (e.g. blood plasma)
● Hydrophilic substances dissolve in water
2.2.2. Uses of water
The significance of the physical properties of water
Properties of water
Significance for living things
Liquid at room temperature
∙ Liquid medium for living things and for the
chemistry of life
Much heat energy is needed to raise
the temperature of water
(very high specific heat capacity)
∙ Aquatic environments are slow to change
temperature
Evaporation of water requires a great
deal of heat
(high latent heat of vaporisation)
∙ Evaporation of water in sweat or in
transpiration causes marked cooling
∙ Much heat is lost by the evaporation of a
small quantity of water
Much heat must be removed before
freexing occurs
(very high latent heat of fusion)
∙ Contents of cells and aquatic environments
are slow to freeze in cold weather
Ice is less dense than water, even very
∙ Ice forms on the surface of water, insulating
13. cold water
(maximum density at 40C)
the water below
∙ When surface water does freeze, aquatic
life can survive below the ice
Water molecules at surface with air
orientate so that hydrogen bonds face
inwards
(very high surface tension)
∙ Water forms droplets on surfaces and runs
off
∙ Certain small animals exploit surface
tension to land on and move over the
surface of water
Water molecules slide over each other
very easily
(very low viscosity)
∙ Water flows readily through narrow
capillaries
∙ Mucus is used externally to aid movement in
animals (e.g. snail and earthworm). It is also
used internally in the movement of food
along the digestive tract or movement of
sperm along the oviduct.
(ii) The synovial fluid lubricates movement in
many vertebrate joints.
(iii) The pericardial fluid lubricates movement
of the heart.
Water molecules adhere to sufaces
(strong adhesive properties)
∙ With low viscosity, capillarity becomes
possible, water moves through extremely
narrow spaces e.g. between soil particles,
and in cell walls
∙ Large adhesive forces between cellulose in
capillary and the water within them so a
column of water can be maintained (capillary
action)
Water column does not break or pull
apart under tension
(high tensile strength)
∙ Medium for chemical reactions of life
Water is colourless
(high transmission of visible light)
∙ Plants can photosynthesize at depth in
water
∙ Light may penetrate deeply into living
tissues.
Light can easily penetrate the waterfilled
epidermis of leaves and reach the underlying
mesophyll cells, which contain chloroplasts
15. 2.3.2.1. Fatty acids
● A fatty acid consists of a hydrocarbon chain and a hydroxyl group (COOH), i.e. RCOOH, R
being the hydrocarbon chain
● Fatty acids may be saturated or unsaturated
● Saturated fatty acid (e.g. stearic acid)
→ does not contain carboncarbon double bond in hydrocarbon chain
→ have the maximum number of hydrogen atoms
● Unsaturated fatty acid (e.g. oleic acid)
→ contains carboncarbon in double bond hydrocarbon chain
→ kinks in fatty acid tail
2.3.2.2. Glycerol
●
Glycerol’s molecular formula is C3H8O3
2.3.3. Classification of Lipids
● Simple Lipids
→ formed by joining fatty acids to an alcohol (e.g. glycerol) by ester linkages
→ Fats are formed by joining fatty acids to a glycerol molecule.Examples of fats include
monoglyceride,diglyceride and triglyceride.
17. 2.3.3. Functions of Lipids
2.3.3.1. In Mammals
● Water repellent properties – waterproof fur and skin.
● Structural Cell membranes, phospholipids and polar nature
● Electrical insulation – myelin, insulates neurones, impulse transmission more rapid.
● Hormones – steroids e.g. testosterone and oestrogen
● Physical protection – shock absorb, found round delicate organs e.g. kidneys
● Thermal insulation – conducts heat poorly, so insulates. Blubber in diving animals.
● Energy storage: yield twice as much energy compared with carbohydrates and also yield
metabolic water during respiration.
→ Why is triglyceride able to store energy?
A triglyceride molecule is large and uncharged. It is also insoluble in water: Being insoluble, they
can be stored in large amounts. There will not be any great effect on the water potential of
cells. This can prevent it from diffusing out of cells.
2.3.3.2. In Plants
● Attraction – plant scents contain fatty acids
● Waterproofing – wax for the cuticle (not glycerol,different alcohol used)
● Energy storage – Oil droplets in plant cells
2.3.3.3. Other
● Honeycomb beeswax
2.4. Proteins
2.4.1. Properties of Proteins
● sensitive to pH and heat (can be
denatured)
● shape determines its function (e.g.
active site in enzymes)
● contains H, C, H, S
● Made up of amino acids
● there are about 20 types of amino
acids in proteins