Cell Structure

Cell Wall

Plant cells and prokaryotic cells contain a wall like structure surrounding the membrane. It is called the cell wall.

A cell wall around a cell membrane is an important feature of a plant cell. It is absent in an animal cell. It supports the cell membrane and gives additional protection to the cell.

Plants are exposed to extreme environments during summer, winter and monsoon. They need protection against variations in temperature, high wind speed, atmospheric moisture etc. The cell wall provides extra protection to the plant cells in such conditions. You can easily observe a plant cell under the a microscope. You can use the peel of Elodea or Rhoeo to observe the cell wall and other structures in plant cells.

Cell Membrane

A cell membrane or plasma membrane is the flexible boundary of a cell that separates a cell from its surroundings. It is responsible for the shape of the cell. A cell membrane is made up of proteins, fats and lipids. It allows nutrients to enter the cell and allows wastes to be removed from the cell.

It is porous in nature and allows the movement of substances or materials, both inward and outward. However, the movement of substance is highly regulated. Some molecules are allowed in at any time. Other molecules are only admitted at certain times and in limited amounts. Others are not allowed in at all

Cytoplasm

Cytoplasm is the jelly like substance present between the cell membrane and the nucleus. Cytoplasm is like the factory campus where different activities are performed simultaneously. It includes making new molecules like glucose, proteins, fats etc.

It also accounts for breaking of molecules into smaller components and generating energy. Cytoplasm deals with transport of different components within the cell and outside the cell. It contains the organelles tike mitochondria, ribosome, Golgi apparatus etc.

Nucleus

A nucleus is found in all eukaryotic cells; the only exception to this are matured red blood cells in humans. A nucleus to a cell is what a brain is to our body. It controls all the activities of the cell. A nucleus is generally spherical In shape. The nuclear membrane separates the nucleus from the cytoplasm. Like the membrane of the cell, nuclear membrane allows selective movement of substances across itself.

When observed under high magnifying microscope, a nucleus shows a small spherical body called nucleolus. A nucleus also contains thread like network of chromatin. When a cell divides, the chromatin forms rod like structures which are called chromosomes. Each chromosome carries genes which are responsible for some trait or characteristic. Genes transfer these characters from parents to the offspring. A normal human cell except the gamete cells contains 46 chromosomes. One can see the chromosomes only when the cell divides.

A gene is nothing but a sequence of nucleotides (molecules) that expresses a particular trait or a characteristic. A gene is responsible for transmission of characteristics from parents to the next generation.

Mitochondria

Mitochondria are small kidney shaped organelles found in both plant and animal cells. They are the site of various chemical processes which lead to synthesis of energy rich molecules.

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These energy rich molecules are used by cells for doing work. Thus, they are known as the power house of the cell. Mitochondria use oxygen for generating these energy rich molecules. A cell may contain one or more mitochondria.

Ribosomes

Ribosomes are found either attached to the surface of endoplasmic reticulum or scattered in the cytoplasm. They are associated with protein synthesis.

Plastids

Plastids are membrane bound organelles found only in plant cells and are perform various functIons. Some of them contain the green coloured pigment called chlorophyll. These green coloured plastids are celled chloroplasts. Chloroplasts are the sites where the process of photosynthesis takes place. Some plastids are also known to store products such as starch. end while others help in synthesis of many hypes of molecules that are needed as cellular building blocks.

Vacuole

A vacuole is a sac surrounded by a membrane. A cell uses the vacuole for sloe, various substances such as food, enzymes and waste fora short period of time. Vacuoles of animal cells ere much smaller in comparison to those In plant cells.

Like In an onion cell, a plant cell may show a single large vacuole called centralised vacuole. Vacuoles occupy between 30 % to 90 % of the total volume of the cell. The centralised vacuole present in a plant cell performs various functions: however, Its main function is storage and maintaining the structure of the cell.

Golgi Body

Golgl bodies are generally found located near the nucleus. They modify the proteins made by the ribosomes and help In transporting them to various Organelles and plasma membrane.

Endoplasmic Reticulum

The endoplasmic reticulum Is a network of membranous tubes that connect the cell membrane with the nuclear membrane. The endoplasmic reticulum helps to transport substances in and out of cell. They are often found associated with ribosomes.

Centrioles and Centrosomes

Centrioles and centrosomes are present only in animal cells. They play an important role in the division of the cell.

Lysosomes

Lysosomes are very important and ere also known as suicide begs. Lysosomes contain Substances Net help In digestion of foreign bodies and worn out cell pans.

Hence. when necessary they can digest the entire contents of the nail. In this process all lysosomes also get destroyed.