B2.3 - Cell Specialisation

Specialised cell examples (humans)

• Muscles

• Lungs

• Eggs

• Sperm

Specialised cell examples (plants)

• Root cells

Stem cells

Versatile, unspecialised cells within an organism that can either specialise or remain stem cells to facilitate development of new cells

Stem cells plants example

Meristematic tissue - found in buds and stems, can differentiate into any type of tissue

Cell reproduction allows

Growth, replacement of dead/damaged cells

Zygote development + specialisation

The cells are initially unspecialised but differentiate quickly, which is a result of genes being expressed. Every cell contains all the genetic information needed to create the whole organism.

Cell signalling

Process of information being transferred from cell surface to nucleus. Signalling controls gene expression and thereby differentiation.

Morphogens

Signal molecules that control cell differentation - found in gradients in different regions of early embryos. The concentration of them dictates regional development within the embryo. The gradient of them results in different parts of the embryo developing different features.

Specialised cell reproduction

Some cells partially or entirely lose the abolity to reproduce when they become specialised (nerve and muscle cells) while others retain the ability, reproducing the same type of cells (skin and epithelial cells)

Stem cells self-renewal

The ability of stem cells to reproduce more stem cells and continue reproduction indefinitely

When do cells become differentiated?

When cell signalling ensures that specific genes are expressed in the cell

Stem cell niche examples humans

Hair follicles and bone marrow

What do stem cell niches have in common?

Signalling factors that bring about both self-renewal and differentiation

Totipotent cells

Only exist in very early embryonic stages. Capable of continuous division, can produce any tissue in the organism. Can form a complete organism

Pluripotent cells

Also only exist in early embryonic stages. Can mature into almost all cell types within an organism, but cannot form a complete organism.

Multipotent cells

Able to differentiate into several cell types, but only in closely related areas. I.e hair follicle cells, which are associated with oil glands, hair, skin and nail reproduction, etc.

Unipotent cells

Form in the late embryonic stage, only forms a single cell type (i.e sperm cells)

Are stem cells visibly distinguishable by their appearance?

No, only by their behaviour

How could stem cells help cure certain diseases/illnesses?

By replacing depleted differentiated cells lost to injury or disease (such as brain or muscle cells)

What determines cell size?

Cell function, cell division apparatus

Smallest human cell?

Sperm cell - all they do is carry genetic material to form a zygote

Largest human cell?

Nerve cell

Red blood cell adaptations

• Concave shape - increases surface area

• Contain haemoglobin which can bind with/release oxygen

• No nucleus or mitochondria

• Smaller, can travel through narrow capillaries

Why are white blood cells larger?

Neccesity for nucleus, granules, and organelles, as well as more enzymes which break down pathogens

Axons

Long fibres in nerve cells which carry impulses up and down the body pver long distances

Why are nerve cells so long?

To efficiently transmit impulses from the brain throughout the body

Functions of (dependent on) cell volume

• Rate of heat and waste production

• Rate of resource production

Function of (dependent on) surface area

Movement of materials in and out of cells

Why are cells so small?

Cells are limited by the size they can reach and still (efficiently) carry out functions of life. Therefore, larger organisms have more rather than larger cells.