Revision: The Fundamental Unit of Life Science English Medium Class 9 CBSE

1. It has no true nucleus.
2. This type of nucleus is called a nucleoid.
3. No nuclear membrane is around the nucleoid.
4. It is ranging from 0.003 to 2.0 micrometers in diameter.

The non-living parts of a cell, i.e., vacuoles and granules, are called cell inclusions.

The living parts of a cell which consist of cytoplasm, nucleus and other living bodies are collectively called protoplasm or protoplast.

Organelles are the specialised and membrane-bound, living structures in a cell concerned with definite functions.

Protoplasm or living matter is a complex semifluid mass of various biochemicals that are often compartmentalized to perform different functions of life.

Nucleoplasm, also known as nuclear sap or karyoplasm, is the gel-like fluid inside the nucleus of a cell. It surrounds and supports the nucleolus and chromatin, helping to maintain the shape and structure of the nucleus and enabling the movement of materials within it.

The nucleoplasm contains a network of dark-coloured fibres called chromatin fibres.

The part of the cytoplasm other than the organelles (mitochondria, etc.) is called cytosol, which constitutes mainly the liquid medium. 

Cytosol is the fluid portion of the cytoplasm inside a cell, excluding organelles. It is a gel-like substance composed mainly of water, salts, and proteins, where many cellular processes such as metabolism and signal transduction occur.

Cell division is one of the most fundamental characteristics of life. This is the method which enables life to perpetuate generation after generation.

The centrosome (in animal cell) splits into two along with the simultaneous duplication of the centrioles contained in it. The daughter centrioles move apart and occupy opposite "poles" of the cell. Each centriole is surrounded by radiating rays and is termed an aster (aster : star).

1. Organelles are membrane-bound, living structures within a cell, each with specific functions—like organs in the body.
2. Protoplasm includes the cytoplasm, nucleus, and all living parts of the cell; protoplast refers to a plant cell without its cell wall.
3. Most organelles are common to both plant and animal cells, except for chloroplasts and cell wall (plant only) and centrosome with centrioles (animal only).
4. Major organelles include nucleus, nucleolus, mitochondria, endoplasmic reticulum, ribosomes, Golgi bodies, and lysosomes.
5. Non-living components, such as vacuoles and granules, are called cell inclusions.

1. The cell membrane (plasma membrane) is the outermost layer in animal cells and lies next to the cell wall in plant cells.
2. It is a thin, flexible, living membrane made of lipoproteins with fine pores.
3. It is semi-permeable, allowing selective substances to pass while blocking others.
4. It separates the cell’s contents from the external environment.
5. It regulates entry of solutes and ions and maintains cell shape (especially in animal cells).

1. The cell wall is the outermost non-living layer in plant cells, surrounding the plasma membrane.
2. It is rigid, non-living, and primarily made of cellulose.
3. It is freely permeable, allowing free movement of substances in solution.
4. It provides rigidity and a definite shape to the plant cell.
5. It protects the cell and supports structural strength.

1. The nucleus is the largest, spherical organelle located centrally in the cytoplasm, enclosed by a double-layered membrane with pores.
2. It contains nucleoplasm, one or more nucleoli, and a network of chromatin fibres.
3. Nucleolus produces ribosomes and assists in protein synthesis by forming and storing RNA.
4. Chromatin fibres (made of DNA) condense into chromosomes during cell division and carry hereditary information.
5. The nucleus controls all cell functions, and its removal leads to cell death.

1. Cytoplasm lies between the cell membrane and the nucleus, excluding the nucleus itself.
2. It is a semi-liquid medium containing water, solutes, and various organelles.
3. The cytosol is the fluid part of the cytoplasm, excluding organelles.
4. Site of all metabolic activities, including enzyme-catalyzed reactions.
5. It supports the functions of organelles and is the medium for glycolysis (anaerobic respiration phase).

1. ER is a network of double-membraned tubules that extend between the plasma and nuclear membranes.
2. It occurs in two forms: Rough ER (RER) with ribosomes and Smooth ER (SER) without ribosomes.
3. RER is involved in protein synthesis and transport because it contains attached ribosomes.
4. SER is responsible for fat (lipid) synthesis and transport.
5. ER provides a supportive internal framework within the cell.

1. The Golgi apparatus, also called dictyosomes in plant cells, is found as stacks of flattened membrane sacs.
2. It consists of cisternae, vesicles, and vacuoles.
3. Involved in the synthesis and secretion of enzymes, hormones, and other substances.
4. Plays a role in the packaging and transport of cellular products.
5. In animal cells, it helps form the acrosome of sperm cells.

1. Lysosomes are membranous sacs formed from the Golgi body.
2. They contain around 40 different types of digestive enzymes.
3. Responsible for intracellular digestion and destruction of foreign substances.
4. Help break down worn-out organelles—hence known as "suicide bags".
5. Aid in digesting cartilage during bone formation.

1. Mitochondria are double-walled organelles, usually sausage-shaped, with inner folds called cristae.
2. They have their own DNA and ribosomes, enabling some self-functioning.
3. Known as the powerhouse of the cell, they produce ATP through aerobic respiration.
4. Responsible for the release of energy from pyruvic acid formed in the cytoplasm.
5. Involved in the synthesis of respiratory enzymes.

1. Plastids are present only in plant cells and are of several types—chloroplasts, leucoplasts, and chromoplasts.
2. They are double-membraned organelles with a proteinaceous matrix and contain DNA.
3. Chloroplasts (green) contain chlorophyll in thylakoids and perform photosynthesis.
4. Leucoplasts are colourless, store starch, and have no pigment.
5. Chromoplasts are variously coloured, contain pigments like xanthophyll and carotene, and help in pollination by attracting pollinators.

1. Vacuoles are clear spaces containing water or dissolved substances, enclosed by a membrane called the tonoplast.
2. Plant cells have fewer but larger vacuoles, while animal cells have smaller ones.
3. Vacuoles store water, food, pigments, and waste, and help maintain cell turgidity.
4. Some vacuoles contain pigments like anthocyanins (violet-blue).
5. Granules are non-living particles (starch, glycogen, fats) that serve as food reserves for the cell.

• Cell division is a vital process for growth, repair, and the formation of new organisms, helping maintain life in all living beings.
• It occurs in two forms: mitosis (in somatic and stem cells) for producing diploid identical cells, and meiosis (in germ cells) for forming haploid gametes.
• Mitosis supports body growth and tissue repair, while meiosis ensures genetic variation and maintains chromosome number in reproduction.
• Before division, the cell’s chromosome number doubles (e.g., from 2n to 4n) to ensure accurate distribution during mitosis or meiosis.