Cell Differentiation and Division

Learning Objectives You will have been successful if by the end of this lesson you can: Describe and explain how cells are specialised to carry out their function Explain the importance of differentiation in plant and animal cells Describe the importance of cell division. Describe the main stages of the cell cycle and the events of mitosis

Not all cells are equal! These show basic animal and plant cells

Cells become specialised All living organisms must be able to carry out the main features of MRSGREN Movement Respiration Sensitivity Growth Reproduction Excretion Nutrition but individual cells may become specialised to be best at one of those activities. This specialisation is called DIFFERENTIATION

Differentiation

Sperm Cells These are essential for sexual reproduction in animals. There are specialised by having a tail which moves them towards the egg. They have a nucleus with only one set of chromosomes (haploid) compared to other cells which have 2 sets of chromosomes

Nerve Cells These cells are often very long and can carry electrical impulses to and from the brain. Schwann cells surround the axon and insulate the nerve impulse

Muscle Cells These are cells that are specialised for movement. There are three main types of muscle cell. They all contain protein fibres that make the cell shorten and contract or relax and lengthen

Root Hair Cells These are found on the surface of the roots and create a larger surface area for absorption of water and minerals

Xylem Cells in Plants Carry water and minerals from roots to leaves in plants

Phloem Cells Sieve plates between cells

Tissues Organs and Systems After cells specialise they must group together to be effective. This creates a tissue

The tissues will be specialised to perform one role very effectively so different tissues will be required to form organs

Organs have one or more main functions and often many organs cooperate to do a more complex task such as digestion

Levels of organisation in a multicellular organism …………………… - the basic structural and functional unit of a living organism. ……………………… - a group of cells with similar structures, working together to perform a shared function. …………………… - a structure made up of a group of tissues, working together to perform specific functions. ………………… ………………………… - a group of organs with related functions, working together to perform body functions. Tissue Organ Organ System

Cell Division Why do cells divide? What would happen if they didn’t? Organisms would only ever exist as single cells – fine for bacteria but not so good for plants and animals! Old and damaged cells would never be replaced. Organisms wouldn’t reproduce.

Divide and grow Most animals and plants start off life as just a single cell, but grow to become adults containing billions and billions of cells. How does one cell become billions and billions of cells? The type of cell division that makes animals and plants grow is called mitosis. parent cell In mitosis, a parent cell divides into two identical daughter cells. These daughter cells divide in two, and so on. mitosis Mitosis is also the way in old and damaged cells are replaced. daughter cells

DNA, Chromosomes and Genes Chromosomes are made of a material called DNA. Sections of DNA are called genes and each gene carries the instructions to make one protein. Many genes are located on a chromosome.

Duplicating chromosomes A cell’s chromosomes are usually long, thin strands. Just before the cell divides, however, the chromosomes become shorter, thicker and more visible. They are said to condense. Each chromosome duplicates and becomes two strands, each one called a chromatid. The two chromatids are joined at the centromere. condensed chromosome chromatid centromere

In Your Books Copy the diagram and add labels Chromosome Chromatid centromere What material are chromosomes made of? What is the purpose of the centromere? What are small sections of the chromosome that code for a protein called? Give 3 reasons why cells must divide. Chromosome replicates chromatid Chromosome centromere

What happens during mitosis? Teacher notes This six-stage interactive animation shows how a cell divides by mitosis. Suitable prompts could include: Start: What type of cell might be this represent? Stage 1: Where are chromosomes found? Stage 2: What must happen to chromosomes before the cell divides? Stage 3: How do the chromosomes get out of the nucleus? Stage 4: How are the chromosomes separated? Stage 5: What must happen after the chromosomes have been separated? Stage 6: How does each new cell compare with the original?

What are the stages of mitosis? Once the chromosomes have duplicated, mitosis takes place. This is a continuous process but can be divided into several parts: Each chromosome replicates so it contains two identical chromatids. The chromosomes align in the middle of the parent cell. The two chromatids in each chromosome are pulled apart into separate halves of the cell. The cell splits in two to produce two daughter cells, each containing the same chromosomes. Mitosis involves copying a cell and its chromosomes exactly, so it is sometimes called copying division.

Chromosomes during mitosis Teacher notes This drag and drop activity provides the opportunity for informal assessment of students’ understanding of what happens to chromosomes during mitosis.

Your Task Create an animation of mitosis. Film it or produce a 3D model showing the main events. Your parent cell must have 4 chromosomes at the start Use colour to help you show this clearly. You must label the cell and contents. Chromosome Cell membrane Centromere