Cell Tissue Organ and Human Body System

• All organisms are made up of one or more cells and the products of those cells.
• All cells carry out life activities (require energy, grow, have a limited size).
• New cells arise only from other living cells by the process of cell division.

Characteristics of Cells

• Cells provide structure and support to the body of an organism.
• The cell interior is organized into different individual organelles surrounded by a separate membrane.
• The nucleus (major organelle) holds genetic information necessary for reproduction and cell growth.
• Every cell has one nucleus and membrane-bound organelles in the cytoplasm.
• Mitochondria, a double membrane-bound organelle is mainly responsible for the energy transactions vital for the survival of the cell.
• Lysosomes digest unwanted materials in the cell.
• Endoplasmic reticulum plays a significant role in the internal organization of the cell by synthesising selective molecules and processing, directing and sorting them to their appropriate locations.

Basic Components of a Cell

• A. Cell Membrane:
  • Cell Membrane (Animal)
  • Cell Wall (Plant)
• B. Cytoplasm
• C. Nucleus

A. PLASMA MEMBRANE / CELL MEMBRANE:

Structure:

• Jos bilipid membranes.
• A bilipid membranous layer composed of proteins and carbohydrates.
• It is fluid like.
• Selective Permeable Membrane.
• Embedded Proteins within the plasma membrane, with some extending all the way through in order to transport materials.
• Carbohydrates are attached to proteins and lipids on the outer lipid layer.

Functions:

• It separates the cell from its external environment.
• It controls the movement of different substances in and out (selectively permeable).
• It protects the cell and provides stability.

B. CYTOPLASM:

Structure:

• The jelly-like substance is composed of mainly water and found between the cell membrane and nucleus.
• The cytoplasm makes up most of the "body" of a cell and is constantly streaming.

Function: 

• Organelles are found here and substances like salts may be dissolved in the cytoplasm.

C. NUCLEUS:

Diagram: Structures of nucleus diagram

Structure:

• The largest organelle in the cell.
• It is dark and round, and is surrounded by a double membrane called the nuclear envelope/membrane.
• In spots the nuclear envelope fuses to form pores which are selectively permeable.
• The nucleus contains genetic information (DNA) on special strands called (DNA) chromosomes.

Function:

• The nucleus is the "control center" of the cell, for cell metabolism and reproduction.

Cell Membrane

What is Cell Membrane?

The cell membrane, also known as the plasma membrane, is a thin, flexible, and semi-permeable layer that surrounds every living cell. Its main role is to separate the cell from its external environment and to control the movement of substances in and out of the cell.

Key Features of the Cell Membrane:

• Structure: It is mainly made up of a lipid bilayer (two layers of phospholipids) with proteins and carbohydrates embedded in it.
• Selective permeability: Not all substances can pass through it. Only certain molecules are allowed to enter or leave the cell.
• Flexibility: The membrane is soft and elastic, which helps the cell maintain its shape.

Functions of the Cell Membrane:

• It keeps the internal environment of the cell separate from the outside.
• It regulates the exchange of oxygen, water, nutrients, and waste products.
• It allows the cell to communicate with its surroundings and with other cells.
• It protects the cell and helps maintain its shape.

👉 Simply put, the cell membrane works like a gatekeeper of the cell, deciding what can enter and what must leave.

Diagram: structure of the cell membrane diagram

Organelles of Both Plant and Animal Cells

A. "ER" OR ENDOPLASMIC RETICULUM:

Diagram: endoplasmic reticulum diagram

• A network of membranous canals filled with fluid.
• The "Transport System" of the cell.
• Two types of ER:
  • Rough ER: Rough ER is lined with ribosomes and is rough in appearance.
  • Smooth ER: Smooth ER contains no ribosomes and is smooth in appearance.

B. RIBOSOMES:

• Small particles which are found individually in the cytoplasm and line the membranes of the Rough ER.
• Ribosomes produce protein.
• They could be thought of as "factories" in the cell.

C. GOLGI BODY / APPARATUS:

• Golgi bodies are stacks of flattened membranous stacks (they look like pancakes!).
• Temporarily stores protein which can then leave the cell via vesicles pinching off from the Golgi.

D. LYSOSOMES:

• Small sac-like structures surrounded by a single membrane.
• Containing strong digestive enzymes which when released can break down worn out organelles or food.
• Also known as a suicide sac.

E. MITOCHONDRIA:

• Round "tube-like" organelles that are surrounded by a double membrane.
• Inner membrane being highly folded.
• Referred to as the "powerhouse" of the cell as it releases energy from food molecules to the cell, which is called respiration.
• Some cells (e.g. muscle cells) require more energy than other cells and so would have many more mitochondria.

F. VACUOLES:

• Fluid filled organelles enclosed by a membrane.
• Can store materials such as food, water, sugar, minerals and waste products.

The Organelles of cells

The Organelles of cells

Serial	Organelle
a. Nucleus	Stores genetic information in DNA, synthesizes RNA and ribosomes.
b. Mitochondrion	Transfers energy from organic compounds to ATP.
c. Ribosome	Organizes the synthesis of proteins.
d. Endoplasmic Reticulum	Prepares proteins for export (rough ER); synthesizes steroids, re regulates calcium level, breaks down toxic substances (smooth ER).
e. Golgi apparatus	Produces and packages substances produced by the cell.
f. Cell Wall	Supports and protects the cell.
g. Vacuole	Stores enzymes and waste products.
h. Lysosome	Digests molecules, old organelles and foreign substances.

• A rigid organelle composed of cellulose and lying just outside the cell membrane.
• The cell wall gives the plant cell its box-like shape and protects it.
• The cell wall contains pores which allow materials to pass to and from the cell membrane.

• Double membrane bound organelles.
• Plants make and store food in Plastids.
• Found in the cytoplasm and there are two main types:
• Leucoplasts - colorless organelles which store starch or other plant nutrients. (example - starch stored in a potato)
• Chromoplasts - contain different colored pigments. The most important type of chromoplast is the chloroplast, which contains the green pigment chlorophyll. This is important in the process of photosynthesis.

Plant & Animal Cell: Difference

• Plants may have lytic vacuoles, which act like lysosomes in animal cells.
• Although they're not labelled here, plant cells have microtubules and secretory vesicles, too.
• Cell membrane and plasma membrane are just different names for the same structure.

Eukaryotic & Prokaryotic Cell: Difference

Different Parts of Animal Cell

• The "fluid" portion of the cell membrane is made of phospholipids.
• A variety of different proteins are embedded in the bilayer or positioned at its two surfaces. 
  • Transport Proteins.
  • Receptor Proteins.

• Regulate the passage of materials into and out of the cell.
• Allows cells to receive and transmit information.
• Communicate with other cells.

• Everything between the cell membrane and the nucleus is the cell's cytoplasm.
• Cytoplasm consists of two main components:
  • Cytosol and
  • Organelles.
• Cytosol is a jellylike mixture that consists mostly of water, along with Proteins, Carbohydrates, Salts, Minerals and Organic molecules.
• Suspended in the Cytosol are tiny Organelles (Organs).

Tissue

Classification of Tissue

Four types of tissue:

1. Epithelial Tissue
2. Connective Tissue
3. Muscle Tissue
4. Nerve Tissue

1) Epithelial Tissue:

This tissue type forms the external covering or internal linings of body surfaces.

Examples-

• The epithelium of skin (external covering).
• The epithelium of the small intestine (internal lining).
• The epithelium of blood vessels (internal lining).
• The function of epithelial tissues is protection, secretion, and control of permeability.

2) Connective Tissue:

• Tissue that connects, supports, binds, or separates other tissues or organs, typically having relatively few cells embedded in an amorphous matrix, often with collagen or other fibres, and including cartilaginous, fatty, and elastic tissues.
• This is the most diverse type of tissue, but in general it is characterized by having relatively few cells.
• Cells of the connective tissue produce the matrix. There are 4 types of connective tissue based on the nature of the matrix:
• Connective tissue proper (major category of connective tissue)
• Cartilage
• Bone
• Vascular tissue (blood and lymph)

3) Muscle Tissue:

• Muscle cells are specialized for contraction and are responsible for body movements.
• The 3 types of muscular tissue are: 
  • Skeletal / Voluntary Muscle
  • Smooth / Involuntary / Visceral Muscle
  • Cardiac / Heart Muscle

4) Nerve Tissue:

• Nerve cells (neurons) are specialized for conducting electrochemical nerve impulses.
• Nerve cells are easily stimulated and transmit nerve impulses rapidly.
• Groups of nerve cells are held together by connective tissue and collectively make up a nerve.

Systems

What is Nucleus?

• Found scattered throughout the Cytosol, and are relatively Large Organelles.
• The "POWERHOUSE" of the cell.
• Sites of Chemical Reactions that transfer Energy from Organic Compounds to ATP. Energy contained in food is released and converted to ATP.
• The inner membrane has many long folds, known as CRISTAE. The Cristae greatly increases the surface area of the inner membrane, providing more space for the chemical reactions to occur.

• Unlike most other organelles, Ribosomes are not surrounded by a membrane.
• Ribosomes are the site of protein synthesis (Production or Construction) in a cell.
• They are the most numerous organelles in almost all cells. Some are free in the Cytoplasm; others line the membranes of Rough ER.

• Elaboration is deoxyribonucleic acid.
• DNA is a long fiber, like a hair, only thinner and longer.
• It is made from two strands that stick together with a slight twist.
• Proteins attach to the DNA and help the strands coil up into a chromosome when the cell gets ready to divide.

• A chromosome is made up of DNA and the proteins attached to it.
• There are 23 pairs of chromosomes in a human cell.
• One of each pair was inherited from your mother and the other from your father.
• All of the DNA in a cell is found in individual pieces, called chromosomes.

• Molecular geneticists describe Gene as a sequence of DNA nucleotides that usually "code" for polypeptides and eventually into Proteins.
• The genes carry the instructions for making all the thousands of proteins that are found in a cell.
• The genes also determine how the many different cells of a body will be arranged.

• An organ / structure which consists of different types of cells which are responsible for different types of secretion.
• There are two types of gland:
  • Exocrine gland (e.g. Lacrimal gland, Sweat gland)
  • Endocrine gland (e.g. Adrenal gland)

• Most glands of the body are exocrine types with ducts connecting to anatomical surfaces.
• Contrast your salivary glands that open into the oral cavity with sweat glands.
• that deposit their product on the body surface.
• Both types of glands are buried in deeper tissues but their products appear on a surface. Connecting the glands to the surfaces are ducts!

• Endocrine glands are the hormone producing structures of the body.
• Some, like the thyroid are large and others, for instance the islet cells of the pancreas, are small islands of endocrine cells.
• In lacking ducts, endocrine cells release their secretory products into the interstitial spaces around the cells.

• Enzymes are catalysts that make many essential biochemical reactions 'happen' i.e. influences reactions under specific conditions and are not used up or chemically altered in the process.
• They are the basic elements that activate all functions in the body, facilitate reactions that build compounds from the body's raw materials, transport elements throughout the body, break down substances, and eliminate many unwanted chemicals in the body.
• Almost all the enzymes are proteins and each enzyme has a specific metabolic action.
• Their normal activity depends on their environment and any abnormal conditions cause reduced activity.

• Anabolism : The synthesis of all compounds needed by the cells.
• Catabolism : The breakdown of molecules to obtain energy.