Differentiation - cell specialisation and cellular organisation

Stem Cells Learning Objectives Define a stem cell as able to turn into any type of cell Know where stem cells are found - in early human embryos State that stem cells are found in adults, in the bone marrow. Explain how stem cells can be used to cure diseases

Learning outcomes You should be able to: Explain the term DIFFERENTIATION Describe how the structure of some specialised plant and animal cells relates to their functions - sperm - red blood cells - nerve cells (neurones - palisade leaf cells

Key Words Photosynthesis guard cells Chloroplasts vacuole ribosomes Mitochondria cell wall / membrane Stomata cytoplasm nucleus

Sponges Sponges are amongst the earliest multicellular animals on Earth (600 million years old) Some cells are tubular, providing pores through which the water can circulate

Sponges Other sponge cells secrete calcium carbonate or silica, which makes a skeleton for the sponge Sponges are multicellular animals like us but... ... the different types of cells are scattered throughout their bodies They have no tissues and no organs A silica ‘spicule’

A North Wales sponge crab Sponges Recently drugs companies have become very interested in sponges! Unable to move sponges cannot run away from predators Instead, they have evolved chemical defenses Some other organisms carry sponges because of this A North Wales sponge crab

Sponges Some of these chemicals show promise as drugs to fight human diseases For example, a compound called halichondrin, derived from Lissodendoryx is being trialled as an anti-cancer drug Another sponge produces a chemical called avarol, which could be used to treat psoriasis

Differentiation and cell specialisation Multicellular organisms consist of many cells – all derived from the single fertilised egg formed from the fusion of egg and sperm Some cells become specialised to perform certain functions = differentiation Cells can differentiate in a number of different ways: - the number of specialised parts - the shape / size of the cell - some of the contents of the cell

Differentiation and cell specialisation Once a human cell has differentiated it cannot change into another type of cell The cells of the early embryo– they can become any of the different types of cells in a human These are stem cells Stem cells: - are unspecialised - can divide repeatedly to make new cells - can differentiate into several kinds of specialised cells

Differentiation and cell specialisation So far, all of the stem cells identified are only able to differentiate into a limited range of cells For example, stem cells in bone marrow can form white or red blood cells but not neurones, or any other kind of cell There is much interest in stem cells, as they could cure many diseases For example, Parkinson’s disease is caused by the death of a particular group of cells in the brain, which could be replaced using stem cells

Specialised animal cells Red blood cells transport oxygen in the blood They have a very short life-span: every second, 10 million old erythrocytes are destroyed in your spleen and 10 million new ones are made They are made from stem cells in the bone marrow, especially in the ribs, vertebrate, pelvis and skull These cells also make white blood cells (leucocytes)– cells that attack and destroy invading microorganisms

Red blood cells transport O2 and CO2 They are very small, to fit through capillaries and get close to cells in body tissues They are packed with haemoglobin, which combines with O2 or CO2 There is no nucleus, to make room for more haemoglobin

Red blood cells The ‘biconcave’ (refresher) shape of erythrocytes provides a high surface area: volume ratio This increases the amount of oxygen and CO2 that can pass into and out of the cell in a certain period of time

White blood cells leucocytes (white cell) They destroy bacteria and other foreign material They move toward bacteria They are the predominant cell in pus!

Multilobed nucleus Cytoplasm

Specialised plant cells Plants do not have stem cells – most of their cells retain the ability to differentiate throughout their lives