B1 - Cell Biology

L1 - Animal and Plant Cells

Plant and animal cells are eukaryotic, they have cell membrane, cytoplasm and genetic material stored within the nucleus.

Bacterial cells are prokaryotic, they are much smaller in comparison to eukaryotic cells, their genetic material is not stored inside of a nucleus.

Most animal cells have:


  • A nucleus
  • Cytoplasm
  • Cell membrane
  • Ribosomes
  • Mitochondria

Most plant cells have:


  • A nucleus
  • Cytoplasm
  • Cell membrane
  • Ribosomes
  • Mitochondria
  • Cell wall
  • Chloroplasts
  • Permanent vacuole

The vacuole is responsible for the holding water and waste substances within the plant cell.

L2 - Prokaryotic Cells

Prokaryotic cells differ from eukaryotic cells, most prokaryotic cells have:


  • Plasmid DNA
  • Single DNA loops
  • Ribosomes
  • Cytoplasm
  • Flagellum(for movement)

L3 and L4 - Microscopy

Magnification = Image size / Actual size

Light microscopes cannot be used to view mitochondria or ribosomes. Electron microscopes offer a much higher level of magnification and resolution than light microscopes. They are much more expensive however.

When using a light microscope, a low setting for the objective lens should be used so that it can be ensures that the specimen is within the microscope's field of view. As well as this, the specimen should be dyed to increase the visibility under the light microscope.

L5 - Specialised cells

Some cells are adapted to suit their purpose/function, such cells include sperm cells, nerve cells, muscle cells, root hair cells, xylem and phloem.

L6 - Cell Differentiation

Stem cells are undifferentiated cells. In plants, these cells are located in the meristem. Cells in the early stage of embryonic development are stem cells. In adults, stem cells can be extracted from multiple sites including the brain and the bone marrow.

Examples of differentiated cells in plants include: the phloem's companion cells (aid translocation), the leaf's spongy mesophyll and the xylem's xylem vessels (cells within lose walls to form hollow tube which aids transpiration).

Examples of differentiated cells in animals include: red blood cells (concave), reproductive cells (sperm and egg; gametes) and muscle cells.

L7 - Chromosomes

Chromosomes are kept in the nucleus of cells, they are made of DNA molecules; each chromosomes carries a number of genes.

Humans have 46 chromosomes within each body cell (23 pairs).

The sex determination chromosomes is the 23rd pair; and XX pair indicates a female, an XY indicates a male.

L8 - Mitosis and the Cell Cycle

During the cell cycle, genetic material is doubled (more organelles such as mitochondria and ribosomes are made). The cells DNA replicates. The DNA condenses into chromosomes and each of these chromosomes duplicate. The chromosomes then split, with one of each chromosome being pulled towards one side of the cell (cell pole).

Finally, the cytoplasm and cell membranes divide, creating two, identical daughter cells.

L10 - Stem Cells in Plants

In plants, stem cells can be found in the meristem (located as root and shoot tips). Plant stem cells can differentiate into any plant cell, and can do this throughout the plant's lifetime.

L9 - Stem Cells in Animals

A stem cell is a type of cell capable of differentiating into numerous different types of cells to suit a function or purpose.

Stem cells extracted from embryos can differentiate into many different human cells, ethical issues arise from using this in practice however. Stem cells can be extracted from adults from within bone marrow, these stem cells can only differentiate into certain human cells (such as blood cells).

L10 & L9 - Cloning

In therapeutic cloning, embryonic stem cells are often used on a patient with the same genes, this means that the stem cells are not rejected by the patient. There a risks to using stem cells on humans: there is a risk of viral disease transmission and there are ethical concerns about the use of these undifferentiated cells.

The cloning of plants has the potential to save plant species from extinction, as well as producing plants that are genetically engineered to be economically preferable and beneficial.

L11 - Diffusion

Diffusion is the net, passive movement of particles from an area of high concentration to an area of low concentration (in favour of the concentration gradient) through a semi-permeable membrane.

Diffusion can happen in gasses and in liquids; the particle move until they are evenly distributed on both sides of the membrane. In the body, diffusion occurs in the small intestine and in the alveoli.

L12 - Rate of Disffusion

Changing the difference in concentration can affect the rate of diffusion; as can changing the surface area or increasing the temperature of the system.

Factors that make an effective exchange surface include: a thin membrane, a large surface area, moist to prevent cells from drying.

L13 - SA to V Ratio

A single celled organism has a relatively large surface area to volume ratio. This allows for molecules to diffuse in and out of the organism with ease.

L14 - Exchange Surfaces

Fish have certain adaptations that aid in gas exchange (their gills have a very large surface area, the capillaries in each gill filament have a large surface area, the capillaries are close to each gill filament).

Root hair cells: Large surface area, many mitochondria

Alveoli: Large number of capillaries provides concentration gradient required, walls are one cell thick

L15 - Osmosis

Osmosis is the diffusion (passive) of water from a dilute solution to a more concentrated solution through a partially permeable membrane.

L16 - Osmosis Req Prac

Method: Three identical objects will be obtained, it will be ensured that they are the same volume. One of these objects will be placed in a test tube with 10cm^3 of water containing a 0.5 mol sugar solution, the next will be 10cm^3 of a 0.25 solution and the next will be placed in 10cm^3 of distilled water.

L17 - Active Transport

Active transport is the movement of molecules against the concentration gradient (area of low to high concentration), this process requires energy so it is not passive.

Long protrusions found on root hair cells increase the surface area of the cells. The soil that surrounds these cells contain a smaller concentration of mineral ions than the concentration within the cell itself, this means that energy is required to transport these ions.

A nerve cell is specialised for its purpose in many ways, nerve cells contain an axon that carries electrical impulses from one part of the body to another, these axons are insulated by myelin which increase the rate of impulse transfer.

Muscle cells are specialised for their purpose as they can contract due to protein fibres within that change the length of the cells. Muscle cells also contain large amounts of mitochondria.

Sperm cells contain half of a persons genetic information. The head of the sperm is known as acrosome, this contains digestive enzymes. Additionally, sperm cells contain many mitochondria which they require to release energy for movement.