Comprehensive Notes on Cell Structure and Organization

Cell Structure and Organization

Cell Components

• Protoplasm: The living substance of a cell. Includes the cytoplasm and the nucleus.

• Cytoplasm: The region of the cell between the nucleus and the plasma membrane. Contains organelles suspended in a jelly-like medium. Composed of organic and inorganic substances. Serves as the medium for biochemical/metabolic reactions and supports/protects cell organelles, providing them with substances from the external environment.

Microscopic Observation of Cells

• Light Microscope Magnification:

  • x100

  • x400

• Specimens Observed:

  • Onion epidermal cell

  • Hydrilla sp. or Elodea sp. epidermal cell

  • Human cheek epidermal cell (stained blue by methylene blue)

Drawings of Specimens

Onion Epidermal Cell

• Cell membrane

• Cytoplasm

• Nucleus

• Cell wall

• Vacuole

Epidermal Cell of Elodea

• Cell membrane

• Nucleus

• Cell wall

• Cytoplasm

• Vacuole

• Chloroplast

Human Cheek Cell

• Cell membrane

• Nucleus (stained blue by methylene blue)

• Cytoplasm

Typical Animal Cell

• Plasma membrane

• Endoplasmic reticulum:

  • Rough ER

  • Smooth ER

• Nucleus:

  • Nuclear membrane

  • Nucleolus

  • Chromatin

• Ribosome

• Golgi apparatus

• Mitochondria

• Lysosome

• Centrioles

• Cytoplasm

• Microtubule

• Vesicle

Typical Plant Cell

• Nucleolus

• Nucleus:

  • Nuclear membrane

  • Chromatin

• Rough Endoplasmic Reticulum

• Tonoplast (Vacuole membrane)

• Vacuole

• Smooth Endoplasmic Reticulum

• Plasma Membrane

• Mitochondrion

• Cell Wall

• Microtubules

• Chloroplast

• Ribosomes

• Golgi apparatus

• Plasmodesmata

Plant Cell Details (Electron Microscope)

• Inner & Outer Membranes

• Grana (stacks of Thylakoid Discs)

• Cell Wall Junction: Between 2 cell walls

• Nucleus:

  • Nucleolus

  • Nuclear Membrane

  • Nuclear Pore

  • Chromatin (DNA)

• Mitochondrion

• Smooth ER

• Chloroplast

• Golgi Apparatus

• Cell Membrane

• Ribosome

• Rough ER

• Central Vacuole membrane

• Large Central vacuole

• Cytoplasm

Cellular Components: Animal and Plant Cells

• Plasma membrane

• Cytoplasm

• Cell wall (Plant cells only)

• Vacuoles

• Vesicles

• Nucleus

• Mitochondria

• Ribosomes

• Endoplasmic reticulum

• Golgi apparatus

• Lysosomes

• Centrioles (Animal cells only)

• Chloroplasts (Plant cells only)

Functions of Cellular Components

Plasma Membrane

• Structure: A thin membrane around the cytoplasm of a cell, selectively permeable, made up of two lipid layers (lipid bilayer).
  Composition: Phospholipid molecules (head and tail), cholesterol, glycoproteins, proteins (receptor proteins, transport proteins), carbohydrates, cytoskeleton.

• Function: Separates a cell from its external environment, holds the cell contents together, controls the exchange of molecules between the cell and its external environment through active transport, passive transport & simple diffusion.

Cell Wall

• Structure: A rigid outer layer surrounding the plasma membrane of plant cells, composed of cellulose (a tough & fibrous carbohydrate).

• Function: Maintains the shape of the plant cell, provides mechanical strength & support, prevents the cell from bursting in dilute solutions.

Cytoplasm

• Structure: A region between the nucleus & the plasma membrane, consists of a jelly-like medium in which the cell's organelles are suspended, contains organic & inorganic substances.

• Function: Acts as a medium for biochemical/metabolic reactions, supports & protects the cell organelles, provides the organelles with substances obtained from the external environment.

Nucleus

• Structure: Largest organelle in the cell, spherical or oval shaped, contains chromosomes, nucleoplasm & nucleolus, surrounded by a double layered nuclear membrane.
  Components: Nuclear envelope, nuclear pore, nucleoplasm, nucleolus, chromatin, DNA.

• Functions:

  • Controls all the cell activities.

  • Nucleolus: Makes ribonucleic acid (RNA) which is needed to make ribosomes.

  • Chromosomes: Contains genetic material, DNA that determines the characteristics of a cell & its metabolic function & also carries information to control the activities of the cell.

  • Nuclear membrane: Separates the contents of the nucleus from the cytoplasm & controls the movement of materials in and out.

Endoplasmic Reticulum (ER)

• Structure: A network of membrane in the cytoplasm that is connected to the nuclear membrane. Consists of Rough ER (RER) & Smooth ER (SER).

• Rough ER (RER):

  • Structure: Is a flat sealed sac that is continuous with the nuclear membrane. Outer surface is covered with ribosomes.

  • Function: Transports proteins synthesized by ribosomes.

• Smooth ER (SER):

  • Structure: An interconnected tubular system, does not have ribosomes.

  • Functions:

    • Synthesizes & transports lipids.

    • Detoxification of drugs and metabolic by-products.

Ribosome

• Structure: Small & dense spherical granules, attached to the outer surface of rough ER or freely suspended in the cytoplasm, made up of ribonucleic acid (RNA) & proteins. Consists of large and small subunits.

• Function: Site of protein synthesis (the instruction required for the synthesis of proteins is stored in the chromatin).

Golgi Apparatus

• Structure: Consists of a stack of flattened membrane-bound sacs.
  Faces: Cis face (incoming), Trans face (outgoing).

• Functions:

  • Processing, modifying & packaging proteins & lipids (e.g., receives protein from rough ER, then modifies & combines the protein with carbohydrate to form glycoproteins then it is packed in a vesicle).

  • Transports & stores lipids.

  • Forms lysosome.

  • Secretes waste product from the cell.

  • Secretes carbohydrates to form the cell walls of plant cells.

Mitochondria

• Structure: Cylindrical or rod shaped, has 2 membranes: an inner membrane & an outer membrane. The inner membrane is folded inward to form the cristae. Contains respiratory enzymes involved in cellular respiration.
  Features: Cristae, matrix, inner membrane, outer membrane.

• Function: Site of cellular respiration to release energy in the form of ATP (adenosine triphosphate) through the oxidation of food substances such as glucose.

Lysosome

• Structure: Spherical sacs surrounded by a single membrane, contain hydrolytic enzymes.
  Components: Single-wall membrane, enzyme complexes.

• Functions:

  • As digestive compartments in a cell.

  • The hydrolytic enzymes digest or break down complex organic molecules such as proteins, nucleic acids, polysaccharides & lipid.

  • Also break down unwanted structures (old organelles or whole cells).

  • In certain unicellular organisms, lysosomes fuse with food vacuoles & release their enzymes into these vacuoles to digest the contents of vacuole.

Centriole

• Structure: Small cylindrical structures that occur in pairs, next to the nucleus in animal cells, composed of a complex arrangement of microtubules.
  Components: Microtubule triplet, connecting fibers, foot, aster, radial fibre (spoke).

• Functions:

  • Form spindle fibres during cell division in animal cells.

  • Synthesizes cilia and flagella which help in the movement of some unicellular organisms such as Paramecium sp.

Chloroplast

• Structure: Biconvex, disc or like lenses shaped, have an inner & an outer membrane, contain chlorophyll.
  Components: Thylakoids, grana, stroma, outer membrane, inner membrane.

• Function: Chlorophyll captures the energy of sunlight and converts light energy into chemical energy during photosynthesis. The green pigment of chlorophyll gives plants their green color.

Vacuole

• Structure: A large sac containing cell sap (water + food + metabolic waste) & surrounded by tonoplast.
  Components: Tonoplast, cell sap.

• Functions:

  • Stores sugars, amino acids & some waste products.

  • Stores colored pigments which give colors to flowers & fruits.

  • Central vacuole in herbaceous plant to give support.

  • Food vacuoles in Amoeba for phagocytosis.

  • Contractile vacuole in Paramecium expels water.

Comparison of Animal and Plant Cells

Unicellular Organisms

• Single-celled organisms able to perform all essential functions (feed, respiration, excrete, move, respond to stimuli, reproduction, and grow).

• Examples: Amoeba sp., Paramecium sp.

Amoeba

• Unicellular animal with pseudopods, lives in fresh or saltwater.

• Pseudopodium: Part of the amoeba used for locomotion.

• Contractile vacuole: Cavity that contracts for osmoregulation.

• Food vacuole: Cavity responsible for digestion.

• Nucleus: Central organelle.

• Living Processes:

  • Locomotion

  • Feeding

  • Respiration

  • Excretion

  • Reproduction

  • Responses to stimuli

  • Growth

• Movement (Amoeboid movement): Extends pseudopodia, cytoplasm flows into the pseudopodium.

• Feeding:

  • Feeds on microscopic organisms (bacteria & diatom).

  • Engulfs food by phagocytosis.

    • Amoeba approaches food particles.

    • Pseudopodia extend and enclose food particles.

    • Food particles are packaged in a food vacuole which fuses with a lysosome containing hydrolitic enzyme (lysozyme).

    • Food particles are digested by lysozyme, nutrients diffuse into the cytoplasm & are assimilated.

    • Undigested material is left behind as it moves away.

Paramecium

• Many species live in freshwater ponds rich in decaying organic matter.

• Components:

  • Cilia

  • Mouth pore

  • Micronucleus

  • Anal pore

  • Food vacuole

  • Macronucleus

  • Contractile vacuole

• Functions:

  • Cilia: Help paramecium move and sweep food into the oral groove.

  • Oral Groove: Collects food, swept into the cell mouth.

  • Anal Pore: Disposes of waste.

  • Contractile Vacuole: Contracts and forces extra water out of the cell.

  • Cytoplasm: Intercellular fluid, helps carry out functions.

  • Gullet: Forms food vacuoles.

  • Food Vacuole: Storage pocket for food.

  • Macronucleus: Larger nucleus, performs normal cell functions.

  • Micronucleus: Smaller nucleus, responsible for cell division.

• Movement: Uses cilia to beat against water, swims forward while rotating on its axis.

Human Cells

• Several types, each adapted to suit specific functions:

  • Nerve cells

  • Muscle cells

  • Red blood cells

  • White blood cells

  • Sperm cells

  • Epithelial cells

Nerve Cell

• Components:

  • Schwann Cells

  • Nodes of Ranvier

  • Dendrites

  • Nucleus

  • Cell Body

  • Axon (with Myelin Sheath)

  • Axon Terminals (Synaptic Bulbs)

  • Synapse

  • Dendrite of Next Neuron

Muscle Cells

• Cardiac muscle cell

• Skeletal muscle cell

• Smooth muscle cell

White Blood Cells

• Eosinophil

• B cell

• Basophil

• Neutrophil

• Band cell

• T cell

• Monocyte

Sperm Cell

• Components:

  • Acrosome

  • Nucleus

  • Head

  • Centriole

  • Mitochondria

  • Axial filament

  • Tail

  • Mid piece

Epithelial Cells

• Composed of closely packed cells of mostly uniform type.

• Cells anchored by a basement membrane.

• Features:

  • Apical or free surface

  • Glycocalyx

  • Tight (impermeable junction)

  • Plasma membranes of adjacent cells

  • Extracellular space between cells

  • Underlying-basement

  • Intermediate (keratin) filaments

  • Anchoring junction (desmosome)

  • Gap (communicating) junction

  • Channel between cells membrane (connexon)

• Gap junctions are found in epithelia, smooth and cardiac muscle, nerve, and certain connective tissues.

Plant Cells (Leaf)

• Palisade mesophyll cells

• Arrangement of cells in a C3 leaf

  • Upper epidermis

  • Palisade mesophyll cell

  • Vein

  • Bundle sheath cell

  • Spongy mesophyll cell

  • Lower epidermis

  • Stoma

  • Guard cells

• Components:

  • Cuticle

  • Upper epidermis

  • Palisade mesophyll

  • Spongy mesophyll

  • Lower epidermis

  • Stoma

  • Guard cells

  • Xylem

  • Phloem

  • Vascular bundle

  • Chloroplast

  • Cell wall

  • Vacuole

  • Nucleus

• Guard cells

  • swollen

  • shrunken

Plant Cells (root/stem)

• Epidermis

• Cortex

• Pith

• Cambium

• Phloem

• Xylem

Xylem Vessels

• spiral

• annular reticulate pitted.

Animal Tissues

• 4 major types:

  • Epithelial tissues

  • Muscle tissues

  • Nerve tissues

  • Connective tissues

Epithelial Tissue

• At the surface of the skin & lining mouth, at the lining of the trachea,lining of small intestine, the lining of kidney tubules, the lining of blood vessel

• Structure:

  • Arranged in one or more layers of cells

  • Cells are tightly interconnected, with little space between them.

  • The structure of epithelial tissues are adapted to its functions.

  • Skin modified to form glands (sweat & sebaceous glands).

  • Small intestine adapted to form mucus secreting goblets.

  • Trachea consists of elongated cell with hair like projections called cillia

  • Alveoli of the lungs are thin, flattened & arranged in single layer

• Function:

  • Carry out functions associated with protection, secretion & absorption

    • Epithelial tissue on the skin

      • Acts as a protective against infections, mechanical injuries & dehydration

      • Secretes sweat & sebum

    • Epithelial tissue in the lining of human intestine

      • Protects the body against pathogens that enter the body through food intake

      • Absorption of digested food

    • Epithelial tissue that lines the trachea

      • Ciliated epithelium traps dust & microbial spores to protect the body against pathogen

    • Epithelial tissues which lines the alveoli of the lungs

      • For gaseous exchange

Types of Epithelial Cells

• Simple squamous

• Simple cuboidal

• Ciliated cell (mucus transport)

• Simple columnar
  Goblet cell

Muscle Tissue

• Smooth muscle tissue

• Skeletal muscle tissue

• Cardiac muscle tissue

• Structure:

  • Composed of cells called muscle fibres

    • Smooth muscle tissue

      • It has a spindle-shaped cell

      • Found along the walls of blood vessels (arteries & veins), alimentary canal, blood vessels, bladder & reproductive tract

      • nucleus located at the centre

    • Skeletal muscle

      • Cylindrical in shaped

      • Attached to the bones by tendon

      • each cell has more than one nucleus

      • Nuclei located at the site

    • Cardiac muscle

      • Found in the heart

• Function:
  * Smooth muscles:
  * Responsible for the involuntary actions of the body, e.g., when the smooth muscles of intestine contract, food is moved along the digestive tract.
  * Skeletal muscles:
  * Responsible for the voluntary movements of the body. Contractions of skeletal muscles produce movements of various body parts.
  * Cardiac muscles:
  * Contract to pump blood to all parts of the body, Contractions of cardiac muscles are involuntary

Nerve Tissue

• Structure:

  • Composed of neurones / nerve cells

  • Each neurone consists of a cell body & nerve fibre called dendrites & axons

• Function:

  • Transmit signals called nerve impulses

  • Control & coordinate activities of the body

• Neuron Components:

  • dendrites

  • axon

  • afferent neurone (sensory neurone)

  • cell body

  • dendron receptor-

  • interneuron (intermediate neuron)

  • node of Ranvier

  • efferent neurone(motor neurone)

  • effector

  • skeletal muscle

• Axon:
  * Long threadlike part of nerve cell
  * Carries nerve impulse away from cell body towards an effector organ
  * Layer of fatty materials insulates the axons of neurons
  * Have gap (nodes of Ranvier)- speed up the transmission of nerve impulse

• Dendron:
  * Threadlike extensions from cell body
  * transmit nerve impulse from other Neurones to cell body
  * consist plasma membrane, cytoplasm & Nucleus As control centre

Connective Tissues

Consist of various types of cells & fibres separated by an extracellular matrix.

• Loose connective tissue:

  • The most widespread connective tissue in the body

  • Consists of a network of collagen, capillaries & spaces filled with fluid.

• **Dense fibrous connective tissue:
  **
  Contains a large number of collagenous fibres which are packed closely together
  * Tendons
  * Ligaments

• Cartilage:
  * Strong & flexible connective tissue

• Bone:
  * a rigid connective tissue
  * consist of cells embedded in a matrix of collagen hardened by mineral deposits such as calcium

• Blood:
  * Consists of red & white blood cells & cell fragments called platelets suspended in a fluid called blood plasma

• Adipose tissue:
  * Consists of tightly packed cells that can be found in the dermis of the skin & around major organs.

• Functions:

  • Bind structures together, & provide support & protection to other tissues.

  • Loose connective tissue:

    • Binds epithelial to underlying tissue & holds organs in place

  • Dense fibrous connective tissue:

    • Forms tendons & ligaments

      • Tendons: attach muscles to bone

      • Ligaments: attach bones to bones

  • Cartilage:

    • provides support to the nose, ears & covers the ends of bones at joints.

    • form discs between vertebrae (cushion to absorb pressure).

    • to keep the trachea & bronchi open

  • Bone:

    • Gives body its shape & support

    • Protects internal organs such as the brain, heart & spinal cord

    • Provides attachment for muscle to enable movement to take place

  • Blood:

    • Transports nutrients & oxygen to cells & removes carbon dioxide & waste products from the cells.

    • Distribute heat throughout the body & contains regulatory substances such as hormones & enzymes.

    • Red blood cells transport oxygen

    • White blood cells assist in fighting infections

    • Platelets aid in blood clotting

  • Adipose tissue:

    • Acts as an energy reserve

    • Insulate the body

Human Organ

Two or more types of tissues work together to form organ. Eg:

Skin: Epithelial + Connective + Nerve + Muscle Tissue
Heart: Epithelial + Connective + Nerve + Cardiac Muscle Tissue

Plant Tissues

Dermal, ground, vascular
Epidermal tissue (dermal)
Ground tissue (Parenchyma, Collenchyma, Sclerenchyma)
Vascular tissue(Xylem, Pholem)

Permanent Tissue

• a mature tissue that has undergone differentiation or are still undergoing differentiation.

Epidermal Tissue

• Structure:

  • Outermost layer that covers the stems, leaves & roots of young plants. flat & have large vacuoles.

  • the walls of epidermal cell which are exposed to air are covered with the cuticle

Ground Tissue

• Is the tissue that pack the spaces between the epidermis & the vascular tissue.

  • Parenchyma tissue:

    • are the least specialised of the cell types found in all the organs of a plant. have thin primary walls & large vacuoles.

  • Collenchyma tissue:

    • Supports non-woody plants, young stems & petioles

    • Thickened by pectin and cellulose

  • Sclerenchyma tissue:

    • have cell walls which are uniformly thickened by lignin & may be dead

Functions of Ground Tissue

• Supports & strengthens plants especially young stems & leaves.

  • Parenchyma tissue:

    • store products of photosynthesis such as sugar & starch. Eg; Parenchyma tissue of sweet potatoes is packed with starch.

    • the palisade mesophyll cells & spongy mesophyll cells in leaves are specialised parenchyma cells which contain chloroplast & carry out photosynthesis.

    • Gives support & shape to plants

  • Collenchyma tissue:

    • An important source of support in herbaceous plants, young stems, leaf stalks & petioles.

  • Sclerenchyma tissue:

    • Support & strengthens the plant body & provides protection to the plant.

Vascular Tissue

Continuous throughout the plant
* Xylem tissue:
* Consists of tracheids & xylem vessels. These are long tubes joined together end to end
* stretching from the roots right up to the shoot
* Cell walls are thickened with lignin which prevents food substances from entering the cells.
* When the cytoplasm disintegrates, a hollow tube is left behinds to allow water minerals to flow easily through the xylem vessel
* Phloem tissue
* Consists of parenchyma cells, sclereids, sieve tubes & companion cells
* the conducting cells are sieve tubes which have pores at both ends, called sieve plates

Function of Vascular Tissue:

• conducts water & dissolved minerals from the roots to the leaves*

• Provides support & mechanical strength to the plant Phloem tissue*

transports organic substances such as carbohydrates & amino acids from the leaves to storage organs & to growing parts of plants.

• Density of different organelles depend on function*

• Sperm-Mitochondria for energy*

• Muscle Cells- lots of Mitochondria to contract & relax*

• Meristematic Cells-Rough ER for cell division*

• Pallisade Mesophyll- Chloroplasts to absorb sun*

• Pancreatic Cells- Rough ER to secrete enzymes*

• Liver Cells-Smooth ER to detoxify*

• Goblet Cells in intestinal epithelium-Secret Mucus( ER & GOLGI APPARATUS)*

Organ Systems Interactions

• Skeletal, Muscular, Respiratory, Digestive, Excretory, Reproductive, and Integumentary systems.

Nervous system

Brain, spinal cord, nerves, detect stimuli/respond with impulses
Coordinate with endoctrine system*

Skeletal system

• Bones support, internal organs, protect muslces*

Circulatory system

transports from cells to exretory organs waste

Respiratory System

nose,trachea,lungs - O2 and CO2

Excretory System

metabolic waste removal CO2 & Urea

Reproductive

Ovaries/Testes to nurtures new organism

Muscular contraction causes body movement*

Endocrine Coordinates and Nerves*.

Lymphatic System

• Protects Infections& returns Flid*.

Integumentary system

Skin Protects from External enviroment.