Fundamental unit of life; cell Flashcards
Types of Cells
Prokaryotic Cells
Cells in which a true nucleus is absent are called Prokaryotic Cells. Since they do not contain any membrane-bound organelle, these are always unicellular organisms, such as Bacteria, Blue-Green Algae, Amoeba, etc.
Eukaryotic Cells
Cells that have a true nucleus are called Eukaryotic Cells. These are complete cells that contain a nucleus, mitochondria, and another membrane-bound organelle. These are always multicellular organisms like animals, plants, fungi, etc.
Structure of cell
Whether prokaryotic or eukaryotic, the cells have a similar structure up to some extent. A variety of key features of the cell are the same. A cell is essentially made up of 4 main components:
Cell Wall and Cell Membrane
Nucleus
Cytoplasm
Cell Organelle
Cell Membrane and Plasma Membrane
It is a biological membrane that separates a cell’s contents from its outside surrounding or external environment.
Properties
Thin-walled, elastic, and semi-permeable
Made up of proteins and lipids
It is a living component of the cell
Functions
Protects the contents of the cell from its external environment
Its semi-permeable allows only selective materials to flow in and out of the cell
Cell wall
The next important topic in our fundamental unit of life class 9 notes is the Cell Wall. It is a structural layer just outside the plasma membrane.
Properties
Flexible, tough, or rigid in some cells
Non-living and freely permeable
Made up of cellulose
Functions
Protects the cell membrane
It is majorly responsible for maintaining the shape and size of the cell
Prevents the cell from becoming flaccid and from drying out.
Nucleus
Nucleus refers to an organelle that is found in eukaryotic cells and contains the genetic material of a cell.
Properties
It is spherical in shape and is enclosed in a nuclear membrane (also known as the nuclear envelope)
Contains a type of protoplasm called nucleoplasm in which the nucleus is suspended
The nucleus contains chromosomes that are made up of proteins and specific molecules of deoxyribonucleic acid or DNA. Chromosomes are, therefore, the carriers of an organism’s genetic information
Functions
Regulates the cell cycle and is responsible for cell division, protein synthesis, growth, etc.
Controls the metabolic activity of cellular components
Controls the genetic characteristics of an organism
Stores hereditary materials in the form of DNA
Cytoplasm
It is a thick, jelly-like substance that is enclosed by the cell membrane and contains all the cell organelles except the nucleus.
Property
The cytoplasm is mainly made up of salts, proteins, and water. This aqueous liquid is called Cytosol.
Function
It facilitates protein synthesis and other metabolic reactions.
Cell Organelle
Golgi Apparatus
Also known as the Golgi body, it is a complex of folded membranes and vesicles found in the cytoplasm of eukaryotic cells. Its function is to modify, sort, and dispatch proteins for synthesis. It also facilitates the formation of lysosomes and the transport of lipids around the cells.
Mitochondria
They are rod-shaped membrane-bound organelles that are responsible for creating the chemical energy to power the biochemical reactions in the cells of most eukaryotic organisms. Since they are the site of cellular respiration and storage centres of ATP (the energy currency of cells), they are often known as the “Powerhouse” of cells.
Ribosomes
The small particles that contain chemical messengers called RNA (ribonucleic acid) and play a major role in protein synthesis.
Endoplasmic Reticulum (ER) A network of membranous tubes (flattened sacs in the cytoplasm) that extend from the nucleus membrane to the plasma membrane of eukaryotic cells. Endoplasmic Reticulum gives internal support to the cell, enables the synthesis of proteins, lipids, and detoxifies any drugs or toxins.
Plastids Membrane-bound organelles are mostly found in plants and are responsible for the plant’s metabolic activities. There are 3 types of plastids that are explained in our fundamental unit of life class 9 notes:
Chloroplasts: Green plastids that contain chlorophyll and help in the production of food through the process of photosynthesis are called chloroplasts.
Chromoplast: Coloured plastids that usually contain yellow and orange colour are referred to as chromoplasts.
Leucoplasts: The colorless plastids which often store starch or oil are known as Leucoplasts.
Vacuoles
Membrane-bound organelles contain liquids or solids. These are permanent and large in plant cells (cover almost 90% of cell space in mature plants). Their main function is to ensure the rigidity of the cell and maintain its osmotic pressure.
Lysosomes
Found mostly in eukaryotic cells of animals, these spherical sac-like structures contain digestive enzymes. They are responsible for breaking down worn-out parts of the cell and destroying any foreign bacteria or viruses. This is why they’re also known as “Suicide Bags”.
Centrosomes and Centrioles
Found only in eukaryotic cells of animals, centrosomes are unbounded organelles that contain centrioles. These are cylindrical microtubes that help in the process of cell division.
Difference between Plant and Animal cells
Plant Cells
A rigid cell wall encapsulates the plasma membrane
Larger than animal cells
Contain plastids
Vacuoles are large and permanent
Do not contain centrosomes and centrioles
Animal Cells No cell wall present Much smaller than plant cells Do not contain plastids (except protozoan Euglena) Vacuoles are small and temporary Do contain centrosomes and centrioles
Osmosis and Diffusion
The flow of water through a semi-permeable membrane is referred to as osmosis. Because the membrane does not allow all molecules to pass through it, osmosis is a selective process. Typically, water is the sole free-flowing molecule across this barrier. For instance, take two flasks and fill one with a mild sugar solution and the other with a highly concentrated sugar solution. A semipermeable membrane separates the two beakers. The water will then flow from the side of the beaker where it is more to the side where it is less. Because it is semi-permeable, or selectively permeable, the membrane enables only water to travel through it and not sugar.
Diffusion, on the other hand, is the transfer of any material from one concentration to another. Diffusion occurs in solids, liquids, and gases, with gases diffusing at a higher pace. This is due to the fact that gas particles are energetic due to their high kinetic energy. Diffusion is the flow of gases into and out of the cell. For example, have you ever noticed the aroma of your favourite dish at home when it is unexpectedly prepared for you by your mother? This is related to the dispersion of the process. When food is prepared in the kitchen, the aromatic molecules from the kitchen begin to move out into the kitchen’s surrounds and, over time, get distributed in the air.
Isotonic, Hypotonic, and Hypertonic Solutions
Isotonic solutions are those that have the same concentration of solutes and pH as the surrounding bodily fluid or cytoplasm.
Hypotonic solutions are those solutions that have a lower solute concentration than the surrounding fluid and can cause the cell to rupture due to an excess of water entering the cell.
Hypertonic solutions are those solutions that have a greater solute concentration than the surrounding fluid and so force water out of the cell, shrinking it.
Who discovered the cell and how?
Under the microscope, Robert Hooke observed cells in thin slices of cork in 1665. He noticed that cork mimics the structure of a honeycomb, which is made up of numerous compartments known as cells.
Why cell is called a structural and functional unit of life?
Because cells are organized in a systematic manner to produce a live entity, we may say that a cell acts as a building block for organisms. Cells are also known as functional units since all of life’s metabolic processes take place at the cell level.
How do substances like carbon dioxide and water move in and out of the cell?
Diffusion allows substances such as carbon dioxide to enter and exit the cell. Substances migrate spontaneously from higher concentrations to lower concentrations. When this movement involves the usage of a semipermeable membrane, it is referred to as osmosis.
How Amoeba obtains its food?
Amoeba receives nourishment through pseudopodia. The amoeba plasma membrane is flexible, allowing the cell to swallow food and create a cup-shaped structure known as pseudopodia through the process of endocytosis.
Which organelle is called as powerhouse of cells and why?
Mitochondria are called so because in it oxidation of food occurs and it produces energy in the form of ATP.
