BIOLOGY - 0654
1- Characteristics of Living Organisms
B1.1 Characteristics of living organisms
Life processes
Movement- an action by an organism causing change of position.
Respiration- the chemical reactions in cells that break down nutrient molecules and release energy for
metabolism.
Sensitivity- the ability to detect or sense stimuli in the internal or external environment and to make
appropriate responses.
Growth- a permanent increase in size and dry mass by an increase in cell number or cell size or both.
Reproduction- the processes that make more of the same kind of organism.
Excretion- removal from organisms of the waste products of metabolism, toxic materials, and substances in
excess of requirements.
Nutrition- taking in materials for energy, growth and development.
Nutrition
Plants require light, carbon dioxide, ions and water.
Animals require organic compounds, ions and usually water.
2- Cells
B2.1 Cell structure
Plant and Animal Cell Parts
Found in both
Nucleus- contains DNA which controls cell activity.
Cytoplasm- gel-like substance made of water that supports internal cell structures. Is the site of metabolic
reactions. Eg. anaerobic respiration.
Cell membrane- holds the cell together, controls what enters and leaves the cell.
Ribosomes- found in the cytoplasm, site of protein synthesis.
Mitochondria- site of most reactions in aerobic respiration, where ATP is released. Cells with high rates of
metabolism (carrying out many cell reactions) have higher numbers of mitochondria.
Only in plant cells
Cell wall- made of cellulose, provides extra support and defines the cell’s shape.
Chloroplasts- contains chlorophyll (to absorb light energy) and the enzymes needed for photosynthesis.
Permanent vacuole- contains cell sap (sugars and salts in water), used to store certain materials and also
helps support the cell’s shape.
Comparing
Both plant and animal cells have a nucleus, a cytoplasm and a cell membrane. In an animal cell the cell
membrane is on the outside of the cell whilst in the plant cell the cell wall covers it.
Only plant cells have a cell wall.
Specialised Cells
Ciliated cells
Found in the respiratory tract, including the middle ear, they move mucus in the trachea and bronchi.
The hairs at the end of the cell beat and push the mucus towards the nose and throat.
Root hair cells
They are extensions of epidermis cells in roots.
The root hair increases sa to volume ratio increasing the rate of absorption.
Palisade mesophyll cells
Found near the top of the leaf, they perform most of photosynthesis.
They contain a lot of chloroplasts to help them.
Red blood cells
Found in the blood, carries oxygen.
Doesn´t have a nucleus to leave space for oxygen. The biconcave shape increases sa to volume ratio.
Sperm and egg cells
The sperm cell has a flagellum to help it swim and enzymes in the head (acrosome) to help it penetrate the
egg.
Page 1 © 2022-2023, Sara Chasserot. All Rights Reserved
,The egg cell has cytoplasm that stores energy and a jelly coat that changes after fertilisation.
Magnification
Magnification= image size / actual size
1 millimetre is 1000 micrometres.
Microscopy
Light microscopes
Rely on light.
Resolution is limited to 0.2nm.
Subcellular structures appear blurry.
● Easy to use
● Relatively cheap
Electron microscopes
Use electrons instead of light.
Max. Resolution is 0.1nm (2000x more than light microscopes).
Can detect sub cellular structures.
● Very expensive
● Hard to use
B2.2 Movement in and out of cells
Diffusion
The net movement of particles from a region of their higher concentration to a region of their lower
concentration down a concentration gradient, as a result of their random movement.
Diffusion helps living organisms to:
● Obtain many requirements like water.
● Get rid of waste products.
● Carry out gas exchange.
Examples of diffusion
Small intestine- digested food molecules from the epithelium to the blood.
Leaf- oxygen from mesophyll cells to mitochondria.
Leaf- co2 from mesophyll cells to chloroplasts.
Leaf- water vapour from stomatal pores to outside the leaf.
Lungs- oxygen from alveolar air gaps to blood capillaries and viceversa with co2.
Energy in diffusion
Particles are always moving randomly (Brownian motion), this generates the kinetic energy used in diffusion.
Factors Influencing Diffusion
The rate of diffusion is how much diffusion occurs in a certain amount of time.
Surface area to volume ratio
The bigger the sa to volume ratio, the faster diffusion happens. Usually the bigger a structure is, the smaller
the sa to volume ratio is, adaptations are developed.
Distance
The smaller the distance, the faster diffusion occurs. This is why blood capillaries’ and alveoli’s walls are one-
cell thick.
Temperature
The higher the temperature, the faster diffusion occurs. The particles have more energy so they bump into
each other more.
Concentration gradient
The greater the difference in concentration, the faster diffusion occurs, on the side with a higher
concentration, more random collisions occur.
Osmosis
The net movement of water molecules from a region of higher water potential to a region of lower water
potential, through a partially permeable membrane.
All cells are surrounded by partially permeable membranes.
Water moves down a concentration gradient.
Examples
Plant- water goes through the cell membrane into the vacuole in a plant cell.
Visking tube- synthetic membrane.
Page 2 © 2022-2023, Sara Chasserot. All Rights Reserved
,Osmosis Experiments
1. Cut cylinders of root vegetables such as potato or radish.
2. Place them into distilled water and sucrose solutions of increasing concentration.
3. The cylinders are weighed before placing into the solutions.
4. They are left in the solutions for 20 - 30 minutes and then removed, dried to remove excess liquid and
reweighed.
If plant tissue gains mass:
Water moved into the plant tissue from the solution, by osmosis.
The solution surrounding the tissue is more dilute than inside.
If plant tissue loses mass:
Water has moved out of the plant tissue into the surrounding solution, by osmosis.
The solution surrounding the tissue is more concentrated than inside.
If there is no mass change:
There has been no net movement and both concentrations must be equal.
Water is still moving in and out but there is no net movement.
Visking tubing
A visking tube is a partially permeable membrane made out of cellulose. It’s not alive.
Osmosis in Plant Cells
When water moves into a plant cell the vacuole gets bigger and makes the cell rigid and firm.
This is crucial so the cells can support the plant and make it stand up.
The pressure created at the cell wall prevents the cell from bursting.
Without enough water the plant wilts.
Water Potential in Animal Cells
As animal cells don’t have a cell wall so osmosis’ effects are more severe.
In a strong sugar solution the animal cell shrivels up as water leaves it (becomes crenated).
In distilled water, there is no cell wall to create turgor pressure so water keeps coming in until the cell is
stretched too far and bursts.
Active Transport
Active transport is the movement of particles through a cell membrane against a concentration gradient
using energy from respiration.
Examples
● Uptake of glucose by epithelial cells in the villi of the small intestine.
● Uptake of ions from soil water by root hair cells in plants.
3- Biological molecules
B3.1 Biological molecules
Food testing
Testing for glucose
Add Benedict’s solution.
Heat in a water bath for 5 minutes.
Positive test shows a colour change from blue to orange/red.
Testing for starch
Add drops of iodine.
Positive test shows a colour change from orange/brown to blue/black.
Testing for protein
Add Bieuret’s solution.
Positive test shows a colour change from blue to violet/purple.
Testing for lipids
Add ethanol and an equal volume of cold water.
Positive test will show a cloudy emulsion forming.
Lipids (fats and oils)
Lipids contain carbon, hydrogen and oxygen.
Lipids are made of triglycerides.
They’re made of 1 glycerol molecule and 3 fatty acid chains.
The fatty acids vary in size.
glycerol phosphate fatty acid chain fat
Lipids are divided into fats (solid at room temp.) and oils (liquid at room temp.).
Page 3 © 2022-2023, Sara Chasserot. All Rights Reserved
, Carbohydrates
Carbohydrates contain carbon, hydrogen and oxygen.
Carbohydrates are long chains of simple sugars.
Carbohydrates can be monosaccharides or polysaccharides.
Polysaccharides are insoluble and not sweet while monosaccharides are soluble and sweet.
Glucose is a monosaccharide, 2 glucoses together form maltose, a disaccharide.
Many glucose together form polysaccharides, some of these are:
● Starch- glucose store in plants.
● Cellulose- material of cell walls.
● Glycogen- glucose store in animals.
Carbohydrates release energy by respiration. Only polysaccharides can be stored.
Proteins
Proteins contain carbon, hydrogen, oxygen and nitrogen.
Proteins are made of amino acids, there are about 20 types.
All proteins have the same basic structure.The amino acids can be arranged in any order, even one small
change results in a new protein.
amino acids / polypeptide chain / protein
Proteins build new tissue, grow and repair. eg. hormones and enzymes.
Water as a Solvent
Water is important as a solvent because many substances can dissolve in it.
Water is important in the following situations:
● Dissolved substances are easily transported around organisms.
● Without water digested food molecules can’t move from the alimentary canal into cells.
● Water facilitates the removal of toxic substances like urea.
● Water makes up 80% of the cytoplasm and is crucial in metabolic reactions.
4- Enzymes
B4.1 Enzymes
Enzymes
Enzymes are proteins that function as biological catalysts, they speed up reactions without being consumed.
They maintain the reaction speed of all metabolic reactions at a rate that can sustain life.
They do different jobs:
● DNA replication- copy a cell's DNA.
● Protein synthesis- hold amino acids in place and form bonds.
● Digestion- digests different food molecules.
Enzymes are specific to a substrate, they have complementary shapes to it as the active site of the enzyme.
1. Enzymes and substrates randomly move in a solution
2. When an enzyme and its complementary substrate randomly collide, an enzyme-substrate complex
forms, and the reaction occurs.
3. A product (or products) forms from the substrate(s) which are then released from the active site. The
enzyme is unchanged and will go on to catalyse further reactions.
Lock and Key
In the lock and key hypothesis, the shape of the active site matches the shape of its substrate molecules. This
makes enzymes highly specific. Each type of enzyme can usually catalyse only one type of reaction (some may
catalyse a few types of reactions).
Enzyme Denaturing
When an enzyme denatures it loses its shape, losing its ability to fit into the substrate.
Denaturation is irreversible.
Things that denature enzymes:
Temperature
Enzymes work fastest at their optimum temperature (37ͦ in the human body).
Heating to higher temperatures than the optimum breaks the bonds holding the shape together (denatured).
Low temperatures don’t denature the enzyme but make it work slower.
pH
Most enzymes´ optimum pH but some have it lower like in the stomach or higher like in the duodenum.
Too high or too low pH denatures the enzyme causing activity to stop.
Page 4 © 2022-2023, Sara Chasserot. All Rights Reserved
