CellsBiologyGCE Study Buddy

A Cell

What is a cell?• A cell is a unit of life• Why must life be organized in cells?• Life requires a structural compartment separate from the

external environment in which macromolecules can perform unique functions in a relatively constant internal environment

• Cells onsists of living matter called protoplasm• A jelly-like substance in which chemical activities are carried out • Consists of 70-90% water, the rest consists of mineral salts and

organic compounds (carbon compounds) such as carbohydrates, fats and proteins

• Its composition varies from animal to animal and from plant to plant

• Consists of 2 forms• Sol (liquid) state• Gel state (semi-solid)

Cell Theory

• all organisms are made up of one or more cells• the smallest organisms are single cells• cells are the functional units of multicellular

organisms • all cells arise from pre-existing cells.

Cell Size• Cells range in size from a few micrometers to several

centimeters• Most cells are small because larger cells do not function

efficiently because small cells can more easily transport materials into and out of themselves.• Advantageous to have a large surface-to-volume ratio• as cell size increases, the volume grows more rapidly

than surface area• The larger the surface area of a cell, the faster a cell

can take in substances and remove waste products.• Whereas large internal volume relative to surface area

makes it more difficult to traffic materials into and out of the cell

How to view cells?• Use microscopes – can magnify cell sizes• Light Microscope (LM)

• Pass visible light through a specimen• Magnify cellular structures with lenses• Magnifies up to 1000x

• Electron Microscope (EM)• Uses a beam of electrons• Has a higher resolving power than the light microscope• Able to magnify more than 1000x• 2 types:• Transmission Electron Microscope (TEM)• Makes it possible to explore call structure.• Beams of electron can only pass through thin samples so cells & tissues

must be cut into ultra thin slices• Scanning Electron Microscope (SEM)• Electrons scan over the surfaces of the specimen.• No need thin slices• Can produce 3-D images.

Animal Cell

Plant Cell

Characteristics of Cells

• A surrounding membrane – Plasma membrane• Protoplasm – cell contents in thick fluid• Organelles – structures for cell function• Control centre with DNA - Nucleus

Protoplasm of a cell consists of:-Cell surface membrane -Cytoplasm where most cell activities occur and contains enzymes and organelles. It can exist in sol or get state-Nucleus which consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin. It controls cell activities and is essential for cell division

Nucleus• Consists of a small spherical mass of denser protoplasm, the

nucleoplasm, surrounded by a nuclear envelope• Controls the normal cell activities• Responsible for cell reproduction• Needed for the continued life of the cell and repair of worn-out parts• Within the nucleus are:• Nuclear envelope: double membrane surrounding nucleus

• Separates the nuclear content from the surrounding cytoplasm• Perforated with thousands of nuclear pores to allow materials to move into

and out of the nucleus to and from the rest of the cell• Nucleoli: spherical structures

• Main function is the production of ribosomes• Chromatin: a network of long thread-like structures (DNA bound to

proteins)• Contain hereditary materials• Control the activities of the cell• During cell division, chromatin threads condense and become highly coiled

structures called chromosomes

Nuclear envelope

What’s in the cytoplasm?

• Cytoplasm: the place where most life processes occur• Embedded in the cytoplasm are important organelles:• Mitochondria: small spherical or rod-shaped

organelles• Involved in release of energy from food substances during cell

respiration

• Chloroplasts• In plant cells only• Sites where plants make food, combining carbon dioxide and

water, using energy from sunlight, to make sugar

What’s in the cytoplasm?

• Vacuoles• In both plant and animal cells• A fluid-filled space enclosed by a membrane• Animal cells may have many small vacuoles but are usually not

permanent.• May contain water and food substances• A plant cell usually has a large central vacuole which contains a

liquid called cell sap• Cell sap contains dissolved substances such as sugars, amino acids, and

mineral salts• This large vacuole is enclosed by a membrane called tonoplast

• Centrioles• Play a part in cell division• Absent in most plant cells

• Ribosomes (2 types)• Free floating ribosomes in cytoplasm• Attached to the Endoplasmic Reticulum

• Ribosomes build all the cell’s proteins• Cells active in protein synthesis are often packed with ribosomes.

• Endoplasmic Reticulum (ER)– Composed of smooth and rough ER– Produces an enormous variety of molecules

• Golgi Apparatus– Works in partnership with the ER– Refines, stores, and distributes the products of cells

What’s in the cytoplasm?

Vacuoles: Lysosomes• Lysosome: a membrane-enclosed sac

– In animal cells– Contains digestive enzymes– The enzymes break down macromolecules

They fuse with food vacuoles to digest the food

They break down damaged organelles

Vacuoles: Central Vacuole

• In plant cells• Membrane bound storage sacs• Contents • Water• Food• Wastes

• Make the cell firm by swelling that helps the plant cell maintain support and rigidity

Endoplasmic Reticulum• Rough ER: The “roughness” is due to ribosomes attached

to the outside of the ER membrane• The functions of the rough ER include

• Produce membrane proteins• Produce digestive enzymes• After the rough ER synthesizes a molecule it packages the

molecule into transport vesicles

• The smooth ER lacks the surface ribosomes of rough ER• Serves many functions:

• Producing proteins• Fatty acids for new membrane synthesis• Produce steroids• Produce sex hormones• Detoxification of drugs and poisons

Mitochondria• Sites of cellular respiration, which involves the production

of energy from food molecules• The matrix contains enzymes which break down

carbohydrates and other nutrients for energy.• The breakdown of these molecules in the presence of

oxygen to produce energy is called aerobic cellular respiration.• Energy releases may be temporarily stored in small

molecules called ATP (adenosine triphosphate) batteries• ATP can be transported from one part of the cell to

another• When needed, ATP break down to release energy

Cell Surface Membrane• Also known as Plasma Membrane• Separates the inside of the cell from the outside environment• Partially permeable to control substances entering or leaving

the cell• Selective permeability• Allowing some substances to cross more easily than others• Block passage of some substances altogether

• Consists of Phospholipid Bilayer• consists of a polar portion, called the head, • and 2 long fatty acids (non-polar), the tail.

Plant Cell Wall

• All plants have cellulose cell walls.• Made up of cellulose fibers.• protect the cell from mechanical damage and help the

cell maintain its rigidity under turgor pressure• prevents over-expansion of the cell when water diffuses into the

cell.• It is a barrier to many fungi, bacteria, and other

organisms that may cause plant diseases.• It is fully permeable to all substances.• bacterial and fungi cells also have a cell wall, but it is not

made of cellulose.

Cell wall vs. Cell membrane

Cell Wall Cell Membrane

A Fully Fully

B Fully Partially

C Partially Fully

D Partially Partially

Q. How permeable are the cell wall and cell membrane in a plant cell?

Animal vs. Plant cells

Plant Cell• Presence of cellulose cell wall• Presence of chloroplast• A large central vacuole• Cytoplasm reduced to a thin

lining• Present of starch grains• Absence of lysosomes

Animal Cell• Absence of cellulose cell wall• Absence of chloroplast• Numerous small vacuoles

(lysosomes)• Cytoplasm fills the cell• Absence of starch grains

Animal vs. Plant cells

Q. Which cell structures are found in plant cells and animal cells?

A.Cell membrane and chloroplastsB.Cell membrane and nucleusC.Cell wall and chloroplastsD.Cell wall and nucleus

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Factory Analogy of a CellCell FactoryCell Wall Factory Wall

Plasma membrane Shipping & receiving Depts

Nucleus the executive department (Manages activities, initiates production, controls activities of factory)

Cytoplasm factory floor where most of the products are assembled, finished, and shipped.

Ribosome assembly line – assemble raw material to manufacture item

Golgi apparatus packaging, shipping, distributing

Endoplasmic reticulum

conveyor belt – move product within factory

Mitochondrion generator – produce energy for the factory

Vacuole store area - store material for later use

Lysosome collection centre – breakdown and recycle used parts

Cell membrane door – allows certain things to enter and leave factory

Specialized cells, tissues, organs, and systems• Types of cells:• Root hair cell:

• Long and narrow shape to increase surface area to volume ratio for efficient absorption of water and mineral salts from the soil

• Red blood cell (erythrocyte)• Contain a red pigment called haemoglobin, enabling the cell to transport

oxygen from the lungs to all parts of the body• Circular biconcave shape to increase surface area to volume ratio so

oxygen can diffuse into and out of the cell at a faster rate• Lacks nucleus, provide more space for haemoglobin.

• Xylem vessels: • Transport water and mineral salts from the roots to the stem and leaves• No cross walls and protoplasm enables water to move easily through

the lumen• Lignin strengthens the walls and prevents collapse of the vessel• When bundled together, xylem vessels provide mechanical support to the

plant

Root hair cell, Red blood cell, Xylem vessels

Xylem vessel: a narrow, cylindrical tube enclosing a continuous space called the lumen. The vessel is dead because there is no protoplasm.

Red blood cells: Flattened, circular biconcave shape to increase the surface area

Root hair cell

Form versus Function• A sphere has the least surface area-to-volume ratio of any

shape.• Cells in multicellular organisms consist of many different types

of cells that do different jobs. • What does it mean for a cell to be specialized?• Specific types of cells performs specific functions

• As cells mature, they may change and differentiate• Differentiation: Process where a cell becomes specialised for a

specific function• Differentiation could target any number of the following:

1. Shape of cell2. Component proteins3. Cell structures or organelles4. Cell growth5. Cell division

• The cell becomes adapted to perform a specific function.

Recap

Cell Function Adaptations

Red blood cell transport oxygen •Circular, biconcave shape•Able to change into a bell shape•Contains haemoglobin•Absence of nucleus

Xylem vessel transport water and mineral salts from roots to stem and leaves.

•Absence of cross walls & protoplasm•Walls strengthened by lignin

Root hair cell absorb water and mineral salts from soil

Presence of long and narrow root hair to increase SA:V ratio

Differentiation is the process by which a cell becomes specialized for a specific function.

Tissues, Organs, and Systems

• Cells of the same type may be grouped together to carry out a special function called simple tissue• Examples:• epithelial tissue: a sheet of cells covering both the

internal and external surfaces of body• plants have similar covering tissues called the epidermis• muscle tissue: a collection of muscle cells which bring

about movement in our body by their contraction and relaxation

• Complex tissue: tissues containing several types of cells • Examples: Nervous tissue, glandular tissue etc

Tissues

Organs

• Different tissues may be united to form an organ eg stomach, liver• An organ is a group of

different tissues working together and enabling the organ to perform a particular functions

Organ System

• Several organs working together for a special purpose make up an organ system• Example: digestive system, respiratory system

• An organism may have a few organ systems.• Plants: stem and leaves as a system• Humans have about 40 organs that are grouped into

about 10 named systems.• The human nervous system includes:• Brain, spinal cord, nerves

Systems

• An organ system is made up of several organs working together for a special purpose. Example: Digestive system

Function: Breakdown and absorb nutrients that are necessary for growth & maintenance

Major organs: Mouth, oesophagus, stomach, small & large intestines

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Human Body Systems• Respiratory System• Takes in oxygen from the surroundings. Removes carbon dioxide and

water vapour into the surroundings• Digestive System• Breaks down the food we eat into simpler substances that can be

absorbed by the blood.• Nervous System• Controls our actions, ensures all the parts of our body work smoothly

together and enables us to respond to changes.• Blood circulatory system• Carries food, oxygen and water to various parts of the body. Carries

wastes away to be removed.• Excretory System• Removes wastes from the body

• Immune System• Defends against infections

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Human Body Systems• Skeletal system• Supports our body, gives us shape, protects our organs and

enables movement.• Muscular system• Enables movement

• Reproductive system• Female Produces eggs for reproduction• Male Produces sperms for reproduction

• Integumentary system (skin)• Waterproof barrier• Regulate temperature

• Lymphatic system• Filters bacteria• Destroy bacteria

• Endocrine System• Secret hormones• Produce response in the body

Plants: Vascular Tissue System• The xylem and phloem that functions in

transport and support; is continuous throughout the plant.