Specialised Cells 3z216n

SPECIALISED CELLS

Specialisation Can you think of any cells which are specialised? How are they specialised, and for what reason? Many organisms are multi-cellular - they are made up of lots of cells, not just one! Many of these cells are specialised, sharing out the life processes. They do one particular job. They develop a distinct shape

Specialised Cells IN ANIMALS

Red Blood Cell

RBC is very small. This helps them to through tiny capillaries RBC is shaped like a biconcave disc. The ‘dent’ in each side of RBC increases the amount of surface area in relation to the volume of the cell. This large surface means that more oxygen can diffuse quickly into the cell.

The cytoplasm is rich in hemoglobin, an ironcontaining molecule that can bind oxygen and is responsible for the red colour of the cells. RBCs have no nucleus, no mitochondria and no endoplasmic reticulum. The lack of these organelles means that there is more room for haemoglobin, so maximizing the amount of oxygen which can be carried by each RBC.

Ciliated epithelial cell

Ciliated epithelial cells present in the respiratory system of human especially in trachea. In between these cells special goblet cells are present which produce mucus. Mucus is a slimy solution; it is sticky and able to trap inhaled dust and bacteria. These cilia sweep the mucus upwards out of the trachea and thus keeps it clean. When mucus reaches top of the trachea it is usually swallowed so that pathogens are destroyed by the acid in the stomach or spit out.

Nerve Cell

They conduct electrical impulses to and from the brain. Nerve cells have a cell body (cyton) and a long thread of cytoplasm called axon. Axon is wrapped by Myelin sheath and acts as insulation that helps in carry impulses much faster. Short threads of cytoplasm are called dendrites bring information to the cell body and axon take electrical impulses from other cells.

Like normal cells nerve cells consists cell membrane, nucleus, mitochondria and other cell organelles to carryout normal cell functions. These are the structural and functional units of nervous system. Some of them are very long and connect distant parts of the body to the spinal cord and brain.

Sperm Cell

Sperm is the male gamete. It consists 3 major parts: Head, Middle piece and Tail Head is having alittle cytoplasm and enzymes. The tip of sperm is called acrosome helps to penetrate into female gamete egg cell during fertilization. Middle piece consists many mitochondria that supply energy to propel sperm through the female reproductive system. The tail of the sperm is a powerful flagellum that whips back and forth, enabling the sperm cell to move. The ATP produced by the mitochondria power the whip like movements of the tail.

Egg Cell

Human egg cell/ovum is non-motile i.e. unable to move themselves It is much larger than sperm cell. Its shape is round and surrounded by membrane which is having a jelly coat on it. Nucleus is located in the center. The cytoplasm consists yolky droplets provides food to nourish the embryo.

Specialised Cells IN PLANTS

Palisade mesophyll cells

These are the cells present in the mesophyll layer of leaf and located just below the upper epidermis. It is the main site of photosynthesis, as there are more chloroplasts per cell. They are long cylinders arranged next to the upper epidermis. This reduces the number of lightabsorbing cross walls in the upper part of the leaf so that as much light as possible can reach the chloroplasts. The cells have a large vacuole with a thin layer of cytoplasm. This restricts the chloroplasts to a layer near the outside of the cell where light can reach them easily. The cell walls are thin, so that gases can diffuse through them more easily.

Root hair cell

A large surface area for absorption of water and mineral ions. Contains lots of mitochondria to provide energy required for absorption of materials by active transport. Membrane with carrier proteins for active transport. Vacuole with high concentration of salts, sugars, solutes to give low water potential. Thin cell wall for short distance for diffusion.

Xylem

These are long, narrow tubes, stretching from the roots, through the stem to the leaves. They are arranged end to end like drain pipes and so helping ascent of water. They do not have cytoplasm and cross –walls so that many cells can form a continuous tube for unimpeded flow of water. The walls of xylem vessels are strong due to lignin present in them which provides . Xylem vessels are part of the vascular bundles which run through the stems of plants like steel reinforcements in concrete pillars. They help to resist bending strains caused by the wind.

Phloem

CELL THEORY All living organisms are made up of cells. Cells are building blocks of living organisms. The cell is the structural and functional unit of life. New cells arise by the division of existing cells. Cells contain inherited information which controls their activities. Given suitable conditions, cells are capable of independent existence.

ORGANISATION IN MULTICELLULAR ORGANISMS