Revision: Cell Structure and Micro-organisms Science SSC (English Medium) 7th Standard Maharashtra State Board

A prokaryotic cell is a simple, single-celled organism that lacks a membrane-bound nucleus and other membrane-bound organelles. Its genetic material is located in the nucleoid region of the cytoplasm.
Examples: Bacteria and Archaea.

Toxin:
The poisonous substances secreted by pathogens that cause diseases are called toxins.

• All living organisms are made up of cells, the basic units of life.
• Cells carry out vital functions necessary for the survival and activity of an organism.
• Organisms typically begin as a single cell, which multiplies through repeated divisions.
• Cells differentiate to perform specific roles, such as support, secretion, and other life functions.
• All cells arise from pre-existing cells and share similar chemical composition and metabolic processes.

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.

• Structure - Double membrane-bound organelle. The outer membrane is smooth; the inner membrane has infoldings called cristae. Inner space is called the matrix.
• Shape & Size - Sausage-shaped or cylindrical. Diameter: 0.2–1.0 µm; Length: 1.0–4.1 µm.
• Function - Site of aerobic respiration; produces energy as ATP. Called the 'Powerhouse of the Cell'.
• Matrix Contents - Contains circular DNA, RNA molecules, and 70S ribosomes for protein synthesis.
• Reproduction - Divides by fission.

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.

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