GCSE Biology Revision Notes
UNIT 1: Tuesday 16 May 9:15-10:30
1.1: Cells
1.2: Photosynthesis and Plants
1.3: Nutrition and Food Tests
1.4: Enzymes and Digestion
1.5: Breathing and Respiration
1.6: Nervous System and Hormones
1.7: Ecological Relationships and Energy Flow
UNIT 2: Friday 9 June 13:30-15:00
2.1: Osmosis and Plant Transport
2.2: Circulatory System
2.3: Reproduction, Fertility and Contraception
2.4: Genome, Chromosomes, DNA and Genetics
2.5: Variation and Natural Selection
2.6: Health, Disease, Defence Mechanisms and Treatments
,1.1: Cells
Animal, Plant and Bacterial Cells
Nucleus – The control centre of the cell. Contains genetic information (DNA) arranged in chromosomes.
Nuclear Membrane – Surrounds the nucleus.
Cell Membrane – A selectively permeable boundary to the cell which allows some substances to enter and
leave the cell but prevents others.
Cell Wall – A fully permeable rigid structure that provides structural support. Made from cellulose (in plant and
animal cells).
Cytoplasm – Jelly-like substance where the chemical reactions of the cell take place.
Large Permanent Vacuole - Contains cell sap and when full pushes the cell membrane against the cell wall,
providing support and turgor.
Mitochondria – Site of cell respiration. Abundant in cells which need lots of energy e.g. muscle cells.
Chloroplasts – Contain chlorophyll, a green pigment that traps light for photosynthesis .
Bacterial cells are single-celled organisms. They:
-Do not contain a nucleus – DNA is a circular chromosome that floats in the cytoplasm
-Have a non cellulose cell wall
-Have many small rings of DNA called plasmids
-Are much smaller than plant and animal cells
,Stem Cells
A stem cell is a simple, unspecialised cell in animals and plants that has the ability to divide to form cells of
the same type and differentiate into a variety of cell types.
In animals stem cells can be harvested from the umbilical cord (embryonic) or bone marrow (adult).
Embryonic stem cells form a full range of cell types while adult stem cells form a limited range of cell types
(e.g. bone marrow stem cells can only form blood cells).
Most animal stem cells change permanently at an early stage into specialised cells with structures that
adapt them to a particular function.
In plants, stem cells originate from meristems at the apices of roots and stems and many of these cells retain
the ability to divide and so can be used in cloning techniques.
Both plant and animal cells can divide and differentiate however plant stem cells can redifferentiate; animal
stem cells cannot.
Benefits of using Stem Cells in Medicine
-Treating leukaemia – chemotherapy and radiotherapy destroy white blood cells in the patient’s body,
stopping their bone marrow producing new blood cells. A bone marrow transplant containing stem cells
from a matching donor allows healthy blood cells to be produced in the patient.
-Stem cells can also be used to replace body parts e.g. organs
Potential Risks of using Stem Cells in Medicine
-Risk of infection from the environment as chemotherapy and radiotherapy leave the patient with no
immune system.
-Stem cells can divide in an uncontrolled manner leading to formation of tumours / development of
unwanted cell types.
-Transfer of viruses or diseases from other animals.
Ethical Concerns with Stem Cells
-In embryonic stem cells, the cells can be taken from an embryo, which is then destroyed. Some call this
murder.
-Some use stem cells to create designer babies.
Peer Review
Peer review is where scientific research is checked by other scientists of at least equal standing – This
ensures any conclusions drawn from scientific investigations are correct. The scientists often provide advice
allowing the research to be improved on.
, Specialisation
Organisms can be:
Single-celled – where all life processes are carried out by one cell.
Multi-celled – where cells differentiate and become specialised to carry out a particular function.
Levels of Organisation
Cell – basic building block of living organisms e.g. animal cell.
Tissue – groups of cells with similar structures and functions e.g. skin.
Organ – groups of different tissues working together to form a structure with a particular function e.g. brain.
Organ System – organs grouped into organ systems e.g. nervous system.
Organism – different organ systems make up the organism e.g. human.
Need for Exchange Surfaces in Multicelled Organisms
As organisms get larger in size their surface area to volume ratio decreases.
As an organism’s volume and surface area increase, their volume will increase much faster. It will eventually
become so large that there is not enough surface area to allow the diffusion of sufficient substances like
oxygen and it will die.
The consequence is that large multicelled organisms need to increase the surface area across which molecule
can diffuse. They do this through the presence of specialised exchange surfaces e.g. lungs in mammals and gills
in fish.
Many types of multicelled organism have also developed transport systems to transport the diffusing
molecules and substances around the body.
Microscopy, Size and Magnification
Making Slides (Practical 1.1)
A slide is a thin piece of glass used to hold objects which are examined under a microscope.
Plant cells:
1. Peel a thin, transparent layer of epidermal cells from the inside of an onion.
2. Place cells on a microscope slide
3. Add a drop of water or iodine (a chemical stain).
4. Lower a coverslip onto the onion cells using forceps or a mounted needle. This needs to be done gently to
prevent trapping air bubbles.
UNIT 1: Tuesday 16 May 9:15-10:30
1.1: Cells
1.2: Photosynthesis and Plants
1.3: Nutrition and Food Tests
1.4: Enzymes and Digestion
1.5: Breathing and Respiration
1.6: Nervous System and Hormones
1.7: Ecological Relationships and Energy Flow
UNIT 2: Friday 9 June 13:30-15:00
2.1: Osmosis and Plant Transport
2.2: Circulatory System
2.3: Reproduction, Fertility and Contraception
2.4: Genome, Chromosomes, DNA and Genetics
2.5: Variation and Natural Selection
2.6: Health, Disease, Defence Mechanisms and Treatments
,1.1: Cells
Animal, Plant and Bacterial Cells
Nucleus – The control centre of the cell. Contains genetic information (DNA) arranged in chromosomes.
Nuclear Membrane – Surrounds the nucleus.
Cell Membrane – A selectively permeable boundary to the cell which allows some substances to enter and
leave the cell but prevents others.
Cell Wall – A fully permeable rigid structure that provides structural support. Made from cellulose (in plant and
animal cells).
Cytoplasm – Jelly-like substance where the chemical reactions of the cell take place.
Large Permanent Vacuole - Contains cell sap and when full pushes the cell membrane against the cell wall,
providing support and turgor.
Mitochondria – Site of cell respiration. Abundant in cells which need lots of energy e.g. muscle cells.
Chloroplasts – Contain chlorophyll, a green pigment that traps light for photosynthesis .
Bacterial cells are single-celled organisms. They:
-Do not contain a nucleus – DNA is a circular chromosome that floats in the cytoplasm
-Have a non cellulose cell wall
-Have many small rings of DNA called plasmids
-Are much smaller than plant and animal cells
,Stem Cells
A stem cell is a simple, unspecialised cell in animals and plants that has the ability to divide to form cells of
the same type and differentiate into a variety of cell types.
In animals stem cells can be harvested from the umbilical cord (embryonic) or bone marrow (adult).
Embryonic stem cells form a full range of cell types while adult stem cells form a limited range of cell types
(e.g. bone marrow stem cells can only form blood cells).
Most animal stem cells change permanently at an early stage into specialised cells with structures that
adapt them to a particular function.
In plants, stem cells originate from meristems at the apices of roots and stems and many of these cells retain
the ability to divide and so can be used in cloning techniques.
Both plant and animal cells can divide and differentiate however plant stem cells can redifferentiate; animal
stem cells cannot.
Benefits of using Stem Cells in Medicine
-Treating leukaemia – chemotherapy and radiotherapy destroy white blood cells in the patient’s body,
stopping their bone marrow producing new blood cells. A bone marrow transplant containing stem cells
from a matching donor allows healthy blood cells to be produced in the patient.
-Stem cells can also be used to replace body parts e.g. organs
Potential Risks of using Stem Cells in Medicine
-Risk of infection from the environment as chemotherapy and radiotherapy leave the patient with no
immune system.
-Stem cells can divide in an uncontrolled manner leading to formation of tumours / development of
unwanted cell types.
-Transfer of viruses or diseases from other animals.
Ethical Concerns with Stem Cells
-In embryonic stem cells, the cells can be taken from an embryo, which is then destroyed. Some call this
murder.
-Some use stem cells to create designer babies.
Peer Review
Peer review is where scientific research is checked by other scientists of at least equal standing – This
ensures any conclusions drawn from scientific investigations are correct. The scientists often provide advice
allowing the research to be improved on.
, Specialisation
Organisms can be:
Single-celled – where all life processes are carried out by one cell.
Multi-celled – where cells differentiate and become specialised to carry out a particular function.
Levels of Organisation
Cell – basic building block of living organisms e.g. animal cell.
Tissue – groups of cells with similar structures and functions e.g. skin.
Organ – groups of different tissues working together to form a structure with a particular function e.g. brain.
Organ System – organs grouped into organ systems e.g. nervous system.
Organism – different organ systems make up the organism e.g. human.
Need for Exchange Surfaces in Multicelled Organisms
As organisms get larger in size their surface area to volume ratio decreases.
As an organism’s volume and surface area increase, their volume will increase much faster. It will eventually
become so large that there is not enough surface area to allow the diffusion of sufficient substances like
oxygen and it will die.
The consequence is that large multicelled organisms need to increase the surface area across which molecule
can diffuse. They do this through the presence of specialised exchange surfaces e.g. lungs in mammals and gills
in fish.
Many types of multicelled organism have also developed transport systems to transport the diffusing
molecules and substances around the body.
Microscopy, Size and Magnification
Making Slides (Practical 1.1)
A slide is a thin piece of glass used to hold objects which are examined under a microscope.
Plant cells:
1. Peel a thin, transparent layer of epidermal cells from the inside of an onion.
2. Place cells on a microscope slide
3. Add a drop of water or iodine (a chemical stain).
4. Lower a coverslip onto the onion cells using forceps or a mounted needle. This needs to be done gently to
prevent trapping air bubbles.
