National 5 Biology | Unit 2 | Key Area 1: Producing New Cells

-Increase in size (of individual cells or whole organisms)

-Increase in cell number (as a result of cell division)

-In multicellular organisms, it allows an individual to increase the number of its cells (ie. growth)

-In multicellular organisms, it allows an individual to replace dead cells

-In some unicellular organisms, it is a method for asexual reproduction

-The process of meiosis (production of sex cells, ie. sexual reproduction)

1. The nucleus divides (mitosis)

2. The cytoplasm divides

Prophase, metaphase, anaphase, telophase

1. Chromosomes in the parent cell replicate and form two chromatids joined by a centromere

2. The nucleus becomes larger

3. Chromosomes shorten and thicken (condense) and become visible for a short time

4. The nuclear membrane breaks down and disappears

1. A spindle appears inside the nucleus (fibres of protein)

2. The chromosomes are lined up across the equator of the cell

3. The chromosomes become attached to the spindle by their centromeres

1. The centromeres of the chromosomes divide, and the half-centromeres repel each other

2. The spindle fibres contract and pull the chromatids of each chromosome apart towards the poles

(Chromatids become chromosomes after they separate)

1. The spindle breaks down

2. The separated chromosomes gather at each pole and new nuclear membrane forms around them

3. The chromosomes uncoil and become invisible again

Divides; cell membrane

It allows one chromosome to consist of two chromatids, so that cell division can occur again. It ensures that each daughter cell receives one identical copy of the genetic information.

46; 23; diploid

One of the chromosome pairs that determine the sex of an individual.

XX

XY

Cells that only have one set of chromosomes from each pair of chromosomes, such as gametes (sex cells, eg. sperm and ova)

Cells that have two matching sets of chromosomes. In humans, there are 23 types of chromosome, and since human cells (apart from gametes) are diploid, we have 46 chromosomes in each cell.

The total number of chromosomes in two complete sets.

Unspecialised cells which can divide to produce new stem cells. They are involved in the growth and repair of the body.

Stem cells can undergo repeated divisions, thus maintaining a pool of unspecialised cells.

Stem cells have the potential to specialise, ie. differentiate into any type of specialised cell in the body.

Stem cells present in the blastocyst (formed after a zygote divides to form a clump of cells). Their function is to produce every cell type needed to make up the human body.

Stem cells found in nearly all tissue types in the human body. Their function is to replace damaged cells and repair damaged tissues.

Differentiate; limited

Bone marrow; brain; heart

Inactive; divide

A group of specialised cells

A group of tissues

A group of organs working together

A group of systems working together

Cells, tissues, organs, systems, organisms