Cell Biology Basics

Introduction to Cell

• Cells are the structural, functional, and biological units of all living beings.
• Cells are the building blocks of life and can replicate themselves independently.
• The entire functioning of living organisms begins from the basic unit called a cell.

Discoveries related to Cell

• Robert Hooke discovered and named the cell in 1665.
• Anton Van Leuwenhoek discovered protozoa and bacteria in 1674.
• Robert Brown discovered the cell nucleus in 1831.
• Schleiden and Schwann proposed the cell theory in 1838 and 1839.
• Purkinje discovered protoplasm in 1839.

Cell Theory

• All living organisms are composed of cells.
• Living organisms can be made up of one or more cells.
• New cells arise from pre-existing cells through the process of cell division.

Cell - different shape, size, and number

• Unicellular organisms are made up of a single cell (e.g., bacteria, protozoa).
• Multicellular organisms are made up of more than one cell (e.g., humans, animals).
• Cells come in different shapes, such as spherical, spindle, and branched and elongated.
• The smallest cell is Mycoplasma (bacteria), and the largest cell is an ostrich egg.

Cell Structure

• The cell consists of components such as the plasma membrane, cell wall, nucleus, cytoplasm, and cell organelles.
• The plasma membrane is the outermost covering of the cell and is selectively permeable.
• The cell wall provides structural strength and lies outside the plasma membrane in plant cells.

Cell Membrane

• The plasma membrane separates the cell contents from the external environment.
• It is selectively permeable, allowing certain materials to enter and exit the cell.
• The plasma membrane regulates the movement of substances in and out of the cell.

Transport Across Cell Membrane

• Passive transport involves the movement of substances from higher to lower concentration without energy.
• Active transport involves the movement of substances from lower to higher concentration with the help of energy in the form of ATP molecules.
• Osmosis is the passage of water molecules across a semi-permeable membrane from a solution with high concentration to a solution with low concentration.
• Types of osmosis include endosmosis (water enters the cell) and exosmosis (water leaves the cell).
• Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration.

Endocytosis & Exocytosis

• Endocytosis is the process of taking in substances through the cell membrane.
• Exocytosis is the process of releasing substances outside the cell through the cell membrane.

Cell Wall

• The cell wall is a non-living, rigid outer covering of plant cells composed mainly of cellulose.
• It provides structural strength and lies outside the plasma membrane.
• Plasmolysis occurs when plant cells lose water through osmosis, resulting in shrinkage of cell contents away from the cell wall.

Lysosomes

• Lysosomes are membrane-bound organelles that contain digestive enzymes.
• They digest foreign material and worn-out organelles to maintain cell cleanliness.
• Lysosomes break down complex substances into simpler ones using powerful enzymes.
• They are also known as "suicide bags" because they may burst during cellular disturbance, leading to self-digestion.

Mitochondria

• Mitochondria are the cell's powerhouses, generating energy in the form of ATP.
• They have two membranes: a porous outer membrane and a folded inner membrane.
• The inner membrane has cristae, which increase the surface area for ATP generation.
• Mitochondria possess their own DNA and ribosomes, enabling protein synthesis.

Plastids

• Plastids are exclusive to plant cells and exist in two varieties: chromoplasts and leucoplasts.
• Chromoplasts are colored plastids, such as chloroplasts, which contain chlorophyll and enable photosynthesis.
• Leucoplasts lack coloration and primarily function as storage sites for starch, oils, and protein granules.

Ribosomes

• Ribosomes are membrane-less cell organelles involved in protein synthesis.
• They are present in both prokaryotic and eukaryotic cells.
• Ribosomes help in the manufacture of protein molecules, enzymes, and hormones.

Vacuoles

• Vacuoles are storage sacs in cells, small in animals and large in plants.
• They are bound by a membrane called the tonoplast.