Key Words

It is important that you know the meanings of all the key scientific words as this will make it easier for you to understand what quesitons are asking and you may be tested on the meanings of some of these.

Look at the words below. Do you know a meaning for each? Click/Tap on the word to check that you know the correct definition.



Different versions of the same gene.


The third stage of mitosis where the centromeres divide and the chromatids move to either pole of the cell.

Anaphase I

Where the homologous pairs of chromosomes separate to different poles of the cell. If there has been any crossing over, recombinant chromosomes are formed.

Asexual reproduction

A reproduction which only involves one parent. This usually occurs because of mitosis. Prokaryotic and other single celled organisms use this type of reproduction.


A connective tissue found on the end of bones (to prevent rubbing) as well as the ear and nose. This tissue is made up of fibres containing elastin and collagen.

Cell cycle

The sequence of events that take place in the cell from formation until it divides to make more cells.

Cell plate

The mechanism by which new plasma membranes and cell walls form in plant cells.


The region which holds two sister chromatids together.


These occur at various parts of the cell cycle to check that the processes at each stage have been carried out correctly. Failure of these have been linked to cancers.


The points at which chromatids break off and rejoins during crossing over.


Two identical DNA molecules.


A chromosome which is unwound in the cell.


The visible strand of DNA seen during cell division.

Ciliated epithelium

Made up of epithelial cells which contain cilia. These beat to move substances – eg in the trachea to move mucus.

Cleavage furrow

This occurs in an animal cell where the cytoplasm starts to divide into two.

Connective tissue

A tissue which holds tissues together or as a transport medium.

Crossing over

Where some of the chromatids between two homologous pairs of chromosomes is broken off and rearranged during creating genetic variation.


Where the cytoplasm divides to make two new cells.

Daughter cells

The cells that are produced as a result of mitosis and meiosis.


The process in which a cell switches off certain genes and becomes specialised. This cell is usually in the G0 phase.

Embryonic stem cells

A source of animal stem cells.


A tissue which covers the outer layers of plants. It contains a waxy impregnation to stop water loss and stomata to allow gases into and out of the plant.

Epithelial tissue

A tissue which covers body surfaces (internal and external).


A red blood cell, this is specialised by being small, flexible and having a large surface area.


Another term for sex cells (sperm and egg).

Guard cells

These cells are found either side of the stomata. They are specialised by having a thick cell wall on one side which affects they shape that they form. They can only carry out the light dependent reaction of photosynthesis.


Where the cell stops growing and comes out of the cell cycle. This could be because the cell has differentiated or the DNA is damaged. This stage may be temporary or permanent.


The first growth phase during which proteins and new organelles are synthesised. The cell increases in size.


Where the cell continues to increase in size, the energy stores are increased and the DNA is checked for errors.

Homologous chromosomes

A matching pair of chromosomes which contain the same genes (but not the same alleles) – eg Chromosome 1 from mum and chromosome 1 from dad would be a homologous pair.

Independent assortment

Where the homologous chromosomes line up in a random order during metaphase I meaning that the daughter cells contain a random mixture of chromosomes from the parent (a complete set but some from mum and some from dad).

Induced pluripotent stem cells

Where a differentiated cell is reprogrammed by switching on certain genes to become a stem cell.


The period of growth and normal working between cell division. This process includes stages G1, G0, Synthesis and G2.

Meristem tissue

A source of stem cells which can be found in the stem of a plant.


A stem cell which can specialise into a range of cells within a certain type of tissue. Eg bone marrow cells can form erythrocytes and a variety of leucocytes.


A tissue which is able to contract and shorten its length. These are 3 main types in the body – skeletal, cardiac and smooth.


Nuclear division used in sexual reproduction to produce 4 haploid daughter cells.

Meiosis I

The first stage of meiosis where the homologous pairs are separated into daughter cells.

Meiosis II

The second stage of meiosis where the pairs of chromatids are separated.


The second stage of mitosis where the chromosomes line up along the equator (sometimes called the metaphase plate).

Metaphase I

Where the homologous pairs of chromosomes line up at the equator of a cell.


Where the nucleus of a cell divides to make two identical nucleuses.


A type of white blood cell which is specialised by having a multi-lobed nucleus that allows it to squeeze through small gaps. Its cytoplasm is loaded with lysosomes.


A group of tissues that perform a specific function in an organism.

Organ system

Groups of organs and tissues which have a major function – eg digestive, cardiovascular and gaseous exchange.

Palisade cell

Found in the mesophyll layer of plants, this specialised cell has a box like structure, a large vacuole and can move its chloroplasts depending on light intensity.


A vascular tissue made up of sieve tubes which have perforated cell walls (called sieve plates) which join cells together. Sugars are transported to all parts of the plant through these.


A stem cell which can differentiate into all the different types of tissue in an organism but not a whole organism (they are present in the early embryo).


The ability of a stem cell to differentiate into specialised cells. The more types of cells it can differentiate into the more potent it is.


The first stage of mitosis where the chromatin condenses to form chromosomes, the nucleolus disappears and the nuclear membrane breaks down and the centrioles migrate to the end of the poles.

Prophase I

Where chromosomes condense, the nuclear envelope disintegrates, the nucleolus disappears and the homologous chromosomes pair up.


A chromatid which has had some of its genetic information altered due to crossing over.

Regenerative medicine

A branch of medicine which uses induced pluripotent stem cells to treat certain diseases.

Root hair cell

This specialised cell has a large surface area to volume ratio, no chloroplasts and lots of mitochondria. It specialises in absorbing water and minerals from the soil.

S Phase

Also known as synthesis phase where the DNA is replicated in the nucleus.

Sperm cell

A specialised cell which is streamlined, contains a tail and numerous mitochondria to take the male nucleus to the egg for fertilisation.

Squamous epithelial tissue

A tissue which is found on the body surface being made up of lots of flat cells.

Stem cell

A cell which has the ability to turn into any other type of cell.


The final stage of mitosis where the chromatids have reached the poles of the cell. The chromosomes start to uncoil and the nucleolus reforms.

Telophase I

When the homologous chromosomes have separated and reached each pole of the cell.


A group of cells with a similar specialised function.

Tissue (adult) stem cells

The stem cells found in tissues which have the ability to turn into a range of cells within that tissue.


A vascular tissue made up of long dead cells whose walls are impregnated with lignin. They transport water and minerals through the plant.


Fertilised egg cell.
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