contents Organization of cell cell tissue organ Difference between plant cell and animal cell Cell structures and their functions: Plasma membrane and its functions Cell wall and its functions Cytoplasm and its functions Golgi apparatus and its functions ER and its functions Lysosomes and its functions Mitochondria and its functions Ribosomes and its functions Nucleus its function and its parts Vacuoles and its functions Difference between prokaryotic and eukaryotic cells
Cellular Organization Cell Tissue– group of cells functioning together. Organ – group of tissues functioning together. Organ System – group of organs functioning together. Organism – group of organ systems functioning together.
cell Cell is the basic structural and functional unit of life. It is the smallest unit of an organism that is classified as living, and is often called the building brick of life.
tissue Group of cells working together constitute a tissue.
organ Group of tissue working together constitute a organ.
Difference between: Plant cell Animal cell
Animal cell Plant cell Animal cells are usually smaller in size. Enclosed by plasma membrane only. Cell wall is absent. Plastids are absent, except in the protozoan euglena. Plant cells are comparatively larger in size. Plasma membrane of plant cells is surrounded by a thick cell wall. Plastids are present.
Animal cell Plant cell Cytoplasm consists largely of smaller vacuole. Nucleus lies in the centre. Prominent and highly complex Golgi bodies present. Animal cells possess centrosome with one or two Centrioles. Cytoplasm peripheral, central space occupied by a large vacuole. Nucleus lies on one side. Contains several sub-units of Golgi apparatus called dictyosomes. Plant cells lack centrosome and Centrioles.
Cell structures and their functions
Plasma membrane This is the outermost covering of the cell that separates the contents of the cell from its external environment. Plasma membrane is a living, thing, delicate, elastic, selectively permeable membrane made up of proteins and lipids and is present in both plants and animals cells.
Functions of plasma membrane It gives definite shape to the cell. It separates the contents of a cell from its surrounding medium. It provides mechanical barrier for the protection of the internal contents of the cell. It is selectively permeable membrane. It regulates the movement of ions in and out of the cell.
Cell wall Plant cells have a rigid outer protective covering called the cell wall which lies outside the plasma membrane. The cell wall is non-living, freely permeable and mainly composed of cellulose.
Functions of cell wall It provides structural strength to the plants cells. It permits the cells of plants, fungi and bacteria to withstand very dilute external media without bursting. It gives a definite shape to the cells. Because of cell walls, plant cells can withstand much greater changes in the surrounding medium than animal cells. Cell wall protects the cells against pathogens and mechanical injury.
It is the fluid part content of the cell which occurs between the plasma membrane and the nuclear envelope. It contains various cell organelles which perform different functions of the cell. Cytoplasm
Functions of Cytoplasm Cytoplasm helps in exchange of material between cell organelles. It acts as a store of vital chemicals such as amino acids, glucose, vitamins, ions, etc. It is the site of certain metabolic pathways such as glycolysis. Synthesis of fatty acids, nucleotides and some amino acids also take place in the cytoplasm.
Golgi Apparatus It is an organelle in animal cells consisting of a set of membrane bound smooth, flattened cisternae stacked one above the other, large spherical vacuoles and small and spherical fluid-filled vesicles. In the plants, Golgi bodies are called dictyosomes. The Golgi apparatus is the secretory organelle of the cell. It arises from the membrane of the smooth ER.
Function of Golgi apparatus Storage, modification and packaging of products in vesicles. Formation of complex sugars from simple sugars. Secretion is the main function of Golgi complex. The secretory proteins and lipids are packed and released on the surface by exocytosis. It helps in the formation of cell plate during cell division. The Golgi apparatus is also involved in the formation of lysosomes and peroxisomes.
Endoplasmic Reticulum The endoplasmic reticulum(ER) is a large network of membrane-bound tubes and sheets extending from outer nuclear membrane to the plasma membrane. It occurs in the three forms- Cisternae, vesicles and tubules. Depending upon the presence and absence of ribosome's on the surface of ER, these are two types- RER with ribosome's attached to its surface for synthesizing proteins.
It gives mechanical support by forming a network in the cytoplasm. ER serves as channels for the transport of materials between various regions of cytoplasm or between the cytoplasm and the nucleus. Certain enzymes present in the smooth ER fats, steroids and cholesterol. Rough ER is concerned with the transport of proteins which are synthesized by ribosome's in their in their surface. Functions of ER
Lysosomes These are membrane-bound vesicular structures found in the cytoplasm of all eukaryotic animal cells expect mammalian RBC’s. Each lysosomes is surrounded by a single membrane and contains powerful digestive enzymes. These enzymes are made by RER. Lysosomes are involved in intracellular digestion of foreign food or microbes and are called digestive bags. These are involved in autolysis of cells after their death, hence they are also called suicidal bags. Lysosomes are a kind of waste disposal system of a cell.
Functions of lysosomes Lysosomes destroy any foreign material which enter the cell such as bacteria and virus, thus protect the cells from infection. They help in removing dead and worn-out cell organelles by digesting them. They bring self-destruction of a cell by releasing their enzymes within the cell. Thus, they act like suicidal bags in damaged cells.
mitochondria These are rod-shaped structures present in the cytoplasm of all the eukaryotes except mammalian RBCs. Mitochondria are called power house of the cells. They store energy in the form of ATP molecules by cellular respiration. It is a self-replicating organelles. They contain DNA, RNA and ribosome's to carry out protein synthesis. Mitochondria are the largest organelles in the animal cells.
Functions of Mitochondria Mitochondria are the sites of cellular respiration. They provide energy for the vital activities of living cells. Mitochondria are able to make some of their own proteins, so they are regarded as semiautonomous organelles. They provide intermediates for synthesis of various chemicals like fatty acids, steroids, amino acid, etc.
Ribosomes They are dense, spherical and granular particles, which occur freely in the matrix or remain attached to the surface of the ER. These are smallest known electron microscopic, ribonucleoprotein particles found in the cytoplasm of both prokaryotes and eukaryotes. Ribosome's are sites of protein synthesis and hence are called protein factories of the cells.
Nucleus Robert brown in 1831 discovered the nucleus is the largest cell structure. It is spherical or oval prominent structure, usually located in the centre of the cell. Nucleus has the following important parts:
Nuclear membrane: it is a double layered membrane, which separates nucleus from the cytoplasm. It haspores called nuclear pores which allow the transfer of material from inside the nucleus to the cytoplasm. Nucleolus: it is a homogeneous and granular dense fluid present inside the nucleus to the cytoplasm. Chromatin material: it consists of long, coiled network of thread-like structures. The chromatin material is made up of DNA which is responsible for storing and transmitting the hereditary information from one generation to the other. It condenses into compact rod-like bodies called chromosomes at the time of cell division. Nucleolus: it is more or less round structure found inside the nucleus. The nucleolus contains RNA and proteins.RNA is helpful in protein synthesis in the cytoplasm.
Vacuoles There are fluid-filled or solid filled membrane bound spaces in cytoplasm. In animal cells, they are small-sized and many, but in plant cells, a single prominent very large vacuole occupies about 50-90% of the cell volume. In the plant cells, vacuole is bounded by a membrane called tonoplast. The vacuole is filled with cell sap which is a watery solution rich in amino acids, sugars, various organic acids and some proteins.
Difference between prokaryotic and eukaryotic cells
Prokaryotic cell Eukaryotic cell
Difference between: Size of the cell is generally small. Nuclear region is poorly defined due to absence of nuclear membrane and known as nucleoid. It contains single chromosome. . Size of the cell is generally large. Nuclear region is well-defined and surrounded by a nuclear membrane. It contains more than one chromosome. Prokaryotic cells Eukaryotic cells
Nucleolus is absent. Membrane bound cell organelles are absent. Cell division takes place by budding. Centrioles absent. Prokaryotic cells are found in bacteria, blue-green algae. Nucleolus is present. Cell organelles such as mitochondria, plastids, ER, lysosomes,etc are present. Cell division occurs by meiotic cell division. Centrioles are present in animals cells. Eukaryotic cells are found in fungi, plant and animal cells.