3.2.1.1 Cell specialisation and organisation

Why do cells differentiate?

To become specialised in structure to suit the function that they will carry out

Root hair cells - structure

• Large SA to absorb a lot of water

• Thin cell wall to allow water to pass through easily

• Doesn’t contain any chloroplasts unlike all other plant cells

Root hair cells - function

Absorbs minerals and water from the soil

Xylem vessels cells

• Xylem cells die during their development and their top and bottom cell walls disintegrate, forming long, empty vessels

• They are very rigid because of hard lignin in their thick side walls, allowing them to withstand high water pressure and support the plant

Phloem vessel cells

• Sieve cells that have a large central channel for sugar to flow through. Forms sieve tubes in the phloem tissue

• Connected together by holes in the cell wall to allow sugar to flow through to the neighbour sieve cells

• Companion cells that are alongside the sieve cells

• They actively pump sucrose into/out of the sieve cells. Pumping in increases the pressure and causes the sucrose to flow either up or down to where it is needed

White blood cells - structure

• Large nucleus

• Can change shape to engulf pathogens

White blood cells - function

• Found in our blood

• They are attracted to pathogens that enter our body

• Some white blood cells engulf any bacteria/disease they encounter so the microbe cannot infect you and make you ill

• Other white blood cells produce antibodies that attach to pathogens making it easier for other white blood cells to engulf them

Nerve cells (neurones) - structure

• Very long cells

• They have axons at one end and dendrons at the other to connect to other nerve cells

• The long axis (main branch) is covered in fat to insulate the electrical impulses, speeding up the messages

Nerve cells ( neurones) - function

To carry nerve impulses (messages) around the body

Sperm cells - structure

• Long tail (flagellum) so they can swim to find an egg

• Lots at mitochondria that create energy for movement

• Made in the testes of males

• Pointed head to burrow into the egg

• Smallest human cell

• It has half of the normal number of chromosomes

Sperm cells - function

To carry the father’s genetic information (DNA) and fuse (fertilise) the egg cell

What do epithelial cells in the intestine do?

They absorb nutrients effiiciently

What are the epithelial cells adaptations?

• Lots of villi on the walls which increase the surface area for absorption, therefore a faster rate of absorption

• Microvilli which increase the SA even more

• Lots of mitochondria to provide energy for the transport of digested food molecules into the cell

Ciliated epithelial cells - structure

• Cells that line the air passages

• Tiny hair called cilia

Ciliated epithelial cells - function

• Prevent lung damage

• Cilia sweep mucus with trapped dust and bacteria back up the throat to be swallowed and destroyed by acid in the stomach

• Tobacco smoke destroys cilia, causing the mucus to build up, leading to smoker’s cough

Egg cells - structure

• Many mitochondria and nutrients in the cell to provide energy to the developing embryo

• The largest human cell

• It has a thick wall, that is broken down by enzymes in sperm, but hardens once a sperm gets in, so no more can enter

• It has half the normal number of chromosomes

• They cannot divide

Egg cells - function

Fuses with a sperm cell and carries the mother’s DNA

Red blood cells - structure

• No nucleus, which increase the surface area

• Contain haemoglobin which picks up oxygen and converts it to oxyhaemoglobin for transport

• Dimpled shape (biconcave disc), which increases the surface area for oxygen absorption

Red blood cells - function

Carry oxygen from the lungs to the body

What is a tissue?

A group of similar cells with a common origin that perform a specific function

What are the 4 types of tissues?

• Connective tissue

• Muscular tissue

• Epithelial tissue

• Nervous tissue

Epithelial tissue

• Covering and lining epithelium

• Found on all surfaces (e.g. skin, blood vessels)

• Consists of sheets of cells

• Lines the surface of organs

• Protective or secretory function

• Many similar types

What is an organ?

A group of tissues that work together to carry out a specific function

Stomach

• Connective tissue to hold together the other tissues

• Muscle to churn and mix the stomach contents

• Epithelium to protect the stomach wall and produce secretion

Leaf

• Palisade mesophyll made up of leaf palisade cells

• Spongy mesophyll adapted for gaseous diffusion

• Epidermis to protect the leaf and allow gaseous diffusion

• Phloem to transport organic materials away from the leaf

• Xylem to transport water and ions into the leaf

What is an organ system?

A group of organs that work together to carry out a specific function