• Plant cell tend to obtain water through osmosis.
Hypotonic solution
If the medium surrounding the cell has a higher water concentration than the cell, the cell will gain water by osmosis. Such a solution is known as hypotonic solution.
isotonic solution
If the medium has exactly the same water concentration as the cell, there will be no net movement of water across the cell membrane. Such a solution is known as isotonic solution.
hypertonic solution
If the medium has a lower water concentration then the cell will lose water by osmosis. Such a solution is known as hypertonic solution.
Plasma membrane or Cell membrane
• This is the outermost covering of the cell that separates the contents of the cell from its external environment.
• The plasma membrane allows or permits the entry and exit of some materials in and out of the cell.
• It also prevents movement of some other materials. The cell membrane is called selectively permeable membrane.
• It is made up of lipid and protein.
→ Properties of Plasma mmembrane
• It is flexible (made up of organic molecules called lipids and proteins).
• Its flexibility enables cell to engulf in food and other from the external environment. This process is called endocytosis. Amoeba acquire food through this process.
→ Functions of Plasma membrane
• It permits the entry and exit of some materials in and out of the cell.
• It prevents movement of some other materials not required for the cell as it acts like selectively permeable membrane.
Cell Wall
• Cell wall is another rigid outer covering in addition to the plasma membrane found in plant cell. The cell wall lies outside the plasma membrane.
• The plant cell wall is mainly composed of cellulose. Cellulose is a complex substance which provides structural strength to plants.
→ Function of Cell Wall
• Cell walls permit the cells of plants, fungi and bacteria to withstand very dilute (hypotonic) external media without bursting.
• In such media the cells tend to take up water by osmosis. The cell swells, building up pressure against the cell wall. The wall exerts an equal pressure against the swollen cell.
• Because of cell wall, cells can withstand much greater changes in the surrounding medium than animal cells.
Plasmolysis
• When a living plant cell loses water through osmosis there is shrinkage or contraction of the contents of the cell away from the cell wall. This phenomenon is known as plasmolysis.
Nucleus
• It is called the brain of the cell as it controls all the activities of cell.
→ Composition of Nucleus
• The nucleus has a double layered covering called nuclear membrane.
• The nuclear membrane has pores which allow the transfer of material from inside the nucleus to the cytoplasm.
• The nucleus contains chromosomes, which are visible as rod-shaped structures only when the cell is about to divide.
→ Functions of chromosomes
• Chromosomes transfer the characters from parents to children in the form of DNA (Deoxyribo Nucleic Acid) molecules.
• Chromosomes are composed of DNA and protein.
Nucleoid
• In some organisms like bacteria, the nuclear region of the cell may be poorly defined due to the absence of a nuclear membrane.
• Such an undefined nuclear region containing only nucleic acids is called a nucleoid.
Cytoplasm
• The cytoplasm is the fluid content inside the plasma membrane.
• It also contains many specialised cell organelles. Each of these organelles performs a specific function for the cell.
→ Function of Cytoplasm
• It helps in exchange of material between cell organelles.
• It act as store of vital chemicals such as amino acid, glucose, vitamins and iron etc.
Endoplasmic Reticulum (ER)
• The endoplasmic reticulum (ER) is a large network of membrane-bound tubes and sheets.
• It is also made up of lipid and proteins.
→ Types of Endoplasmic Reticulum
(i) Rough endoplasmic reticulum (RER)(ii) Smooth endoplasmic reticulum (SER)
→ Functions of Endoplasmic Reticulum
• RER looks rough under a microscope because it has particles called ribosomes attached to its surface. The manufactured proteins are then sent to various places in the cell depending on need, using the ER.
• The SER helps in the manufacture of fat molecules, or lipids, important for cell function.
• Some of these proteins and lipids help in building the cell membrane. This process is known as membrane biogenesis.
Golgi Apparatus
•The golgi apparatus, first described by Camillo Golgi, consists of a system of membrane-bound vesicles arranged approximately, parallel to each other in stacks called cisterns.
• The material synthesised near the ER is packaged and dispatched to various targets inside and outside the cell through the Golgi apparatus.
• It’s function include the storage, modification and packages of products in vesicles.
• It is also involved in the formation of lysosomes.
Lysosomes
• Lysosomes break foreign materials entering the cell, such as bacteria or food as well as old organelles into small pieces.
• They contain powerful digestive enzymes which are made in RER which is capable of breaking down all organic material made in RER.
• when the cell gets damaged, lysosomes may burst and the enzymes digest their own cell. Therefore, lysosomes are also known as the ‘suicide bags’ of a cell.
Mitochondria
• Mitochondria are known as powerhouses of the cell.
• The energy required for various chemical activities needed for life is released by mitochondria in the form of ATP [Adenosine Triphosphate] molecules.
• ATP is known as energy currency of the cell.
• Mitochondria have two membrane coverings instead of just one.
• The outer membrane is very porous while the inner membrane is deeply folded.
• They are able to make some of their own protein.
Plastids
• Plastids are present only in plant cells.
• There are three types of plastids:
(i) Chromoplasts (coloured plastids).
(ii) Leucoplasts (white or colourless plastids).
(iii) Chloroplasts (contains the pigment chlorophyll).
→ Structure of Plastids
• The internal organisation of the plastids consists of numerous membrane layers embedded in a material called the stroma.
• Plastids also have their own DNA and ribosomes like mitochondria and similar to its structure.
→ Function of Plastids
• Chloroplasts are important for photosynthesis in plants.
• Chloroplasts also contain various yellow or orange pigments in addition to chlorophyll.
• Leucoplasts are primarily organelles in which materials such as starch, oils and protein granules are stored.
Vacuoles
• Vacuoles are storage sacs for solid or liquid contents.
• They are small sized in animal cells while plant cells have very large vacuoles.
→ Function of vacuoles
• The central vacuole of some plant cells may occupy 50-90% of the cell volume.
• In plant cells vacuoles are full of cell sap and provide turgidity and rigidity to the cell.
• Many important substance in the life of the plant cell are stored in vacuoles which include amino acids, sugars, various organic acids and some proteins.
• In single-celled organisms like Amoeba, the food vacuole contains the food items that the Amoeba has consumed.
• In some unicellular organisms, specialised vacuoles also play important roles in expelling excess water and some wastes from the cell.
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