Levels of Organisation and Cell Differentiation in Biology

Organelles

Tiny structures inside cells that carry out specific functions.

Nucleus

Controls cell activities and contains DNA.

Mitochondria

Site of aerobic respiration.

Chloroplasts

Site of photosynthesis in plant cells.

Ribosomes

Where protein synthesis occurs.

Cells

The basic unit of life.

Red blood cells

Transport oxygen.

Nerve cells

Carry electrical signals.

Tissues

A group of similar cells working together to perform a specific function.

Muscle tissue

Contracts to produce movement.

Epithelial tissue

Covers surfaces.

Xylem tissue

Transports water in plants.

Organs

A structure made of different tissues working together to perform a specific function.

The heart

Contains muscle tissue, connective tissue, and nerve tissue.

Leaves in plants

Contain palisade tissue (for photosynthesis), xylem, and phloem.

Organ Systems

A group of organs working together to perform a major life function.

The digestive system

Breaks down and absorbs food.

The circulatory system

Transports substances around the body.

Cell Differentiation

The process by which unspecialised cells become specialised for a specific function.

Sperm cell

Streamlined with tail and many mitochondria for swimming and energy.

Root hair cell

Large surface area for absorbing water and minerals.

Neurone

Long with branched ends for transmitting electrical impulses.

Stem cells

Undifferentiated cells that can divide and develop into many different types of specialised cells.

Embryonic stem cells

Found in early embryos and can differentiate into any type of cell (they are pluripotent).

Adult stem cells

Found in bone marrow and some other tissues, can only develop into certain types of cells (e.g., blood cells).

Plant stem cells

Can differentiate into any type of plant cell throughout the plant's life.

Advantages of stem cells in medicine

Can be used to replace damaged or diseased tissues (e.g. spinal injuries, Parkinson's disease, diabetes).

Disadvantages and ethical issues of stem cells

Use of embryonic stem cells involves destroying embryos, which raises ethical and religious concerns.