1. The function of the red blood cell is to transport oxygen from the lungs to the rest of the body.

2. The red blood cell contains a red pigment, named haemoglobin, which binds reversibly to oxygen to form oxyhaemoglobin for oxygen to be transported.

3. Red blood cells have a biconcave shape, which increases the surface area to volume ratio of the cell, which allows efficient diffusion of oxygen in and out of the cell.

4. Red blood cells do not contain a nucleus. The absence of a nucleus allows more haemoglobin to be packed inside the cell, increasing the oxygen carrying capacity of the cell, thus allowing more oxygen to be transported by the cell.

5. Red blood cells have an elastic and flexible cell membrane, which allows the cell to change its shape easily to move through capillaries to deliver oxygen to body cells. (pictured here is a RBC in the lumen of a capillary)

1. The root hair cell functions in the absorption of water and mineral ions*.

2. The root hair cell has a root hair, which is an elongated extension, which helps to increase the surface area to volume ratio of the cell, to increase the rate of absorption of water and mineral ions* via osmosis and active transport respectively.

3. The root hair cell has a large vacuole, which allows more water and mineral ions* to be absorbed and stored.

4. Chloroplasts are also absent in the root hair cell, as it is located underground, and the absence of sunlight make chloroplasts unnecessary.

1. Xylem vessels function to transport water and mineral ions* from the roots up the plant to the leaves.

2. Xylem vessels are hollow and dead, due to the absence of cellular organelles. This allows water and mineral ions* to move through the xylem vessel unobstructed.

3. The walls of the xylem vessel are also deposited with lignin, which is a hard and waterproof substance provides mechanical support to the plant.

4. *note: mineral ions or dissolved mineral salts

The relay neurone (compared to the sensory and motor neruones) is characterised by the the absence of the myelin sheath. The myelin sheath is formed when Schwann cells wrap around the nerve fibres (axons and dendrons) of neurones.

The main function of the relay neurone is to transmit nerve impulses. In a reflex action, the relay neurone transmit nerve impulses from the sensory neurone towards the motor neurone.

The sensory neurone is a myelinated cell. The cell bodies of sensory neurones tend to cluster together to form the swellings known "dorsal root ganglion" of the spinal cord. The axons of the sensory neurones extend into the spinal cord itself.

Sensory neurones function to transmit nerve impulses from the sensory receptors towards the spinal cord.

The sensory neurone is part of the peripheral nervous system (PNS).

The motor neurone is also a myelinated cell. The cell bodies of motor neurones are located within the spinal cord. The axons of motor neurones extend out of the spinal cord.

Motor neurones function to transmit nerve impulses from the central nervous system (CNS) towards the effectors.

Effectors are structures that bring about a response, e.g. muscles that will contract.

The motor neurone is also part of the peripheral nervous system (PNS).

The human sperm is a gamete (sex cell) containing a haploid number of chromosomes in its nucleus found at the head region of the cell.

The middle piece contains large numbers of mitochondria, which function to release energy during aerobic respiration that helps the sperm swim.

The tail of the sperm allows the sperm to swim. Interestingly enough, the sperm tail rotates (it does not move left to right) enabling it to swim. The head of the sperm also spins as its tail rotates.

The human ovum is also a gamete and it also contains a haploid (23) number of chromosomes its nucleus.

The epidermis, is a tissue that is made up of epidermal cells. Usually a single layer of epidermis is found around most plant organs (e.g. roots, stems, leaves).

The epidermis functions to protect the tissues and cells underneath it from mechanical damage or injury.

As its role does not involve photosynthesis, the epidermal cells do not contain chloroplasts. In fact, they are relatively transparent and clear cells, which allow light to pass across these cells readily in order to reach the underlying photosynthetic tissues (palisade mesophyll and spongy mesophyll) in the leaf.

The absence of chloroplasts is also evident when slides prepared with the onion epidermis is viewed under the light microscope.

The phloem itself consists of of the sieve tube element cells and companion cells.

The sieve tube element cells are hollow with sieve plates separating individual cells.

The hollow sieve tube element provides space available for phloem sap to be transported within its lumen.

The process in which manufacture food is transported in the phloem is known as translocation.

The companion cell is closely associated with the sieve tube element. There are large numbers of mitochondria present in the companion cell. Energy is released by the companion cell which aids in the process of loading sugars into the sieve tube element during the process of translocation.

The cytoplasm of the companion cell and its associated sieve tube element are continuous and connected via the plasmodesmata (channel that connects the cytoplasm between two cells).