CELLS: The Building Blocks of Life

CELLS: The Building Blocks of Life

History of the CellHistory of the Cell

• Robert Hooke is a scientist from England.

• He experimented with clocks, telescopes and microscopes.

• He became famous for the observation of thin slices of bark through the microscope in 1667.

• It was this observation that led him to….THE DISCOVERY OF THE CELL !

How did he discover the Cell?How did he discover the Cell?

1. He sharpened his knife as keen as a razor blade.

2. He cut off a very thin piece of cork with his knife.

3. He placed the thin piece of cork on a black object plate.

4. Through the microscope, he observed that the cork cells were perforated and porous, much like a honeycomb.

CORK CELLSCORK CELLS

MicroscopesMicroscopes

•Light microscope can magnify objects up to 1000 x •Thus, many organelles cannot be seen clearly

• Electron microscope

can magnify objects up

to > 200 000x•Thus, many organelles can be seen more clearly

MicrographsMicrographs

What is it?

A camera can be fitted to a microscope to

take pictures. This picture is called the

micrograph.

MicrographsMicrographs

Photomicrograph•Taken using a light microscope•Pictures are in colour

Electronmicrograph• Taken using an electron microscope•Pictures are in black- and-white but images can be artificially colourised.

What does a cell consist of?

cytoplasm

nucleus

cell wall

What does a cell consist of?

What does a cell consist of ?What does a cell consist of ?

Protoplasm

- Nucleus + Cell surface membrane + Cytoplasm

Organelles

- Specialised structures within the cell

Parts of a CellParts of a CellThe protoplasm of a cell is made up of three parts:

Cell surface membrane

• Surrounds the cytoplasm

• Partially permeable

• Hence controls substances entering or leaving the cell

Nucleus

• Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin

• Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

Cytoplasm

• Protoplasm between the cell surface membrane and nucleus

• Where most cell activities occur

• Contains enzymes and specialised structures (organelles)

nucleoplasm nucleolus chromatin nuclear envelope

Cell surface membrane (plasma membrane)

Cell surface membrane

Animal cell Plant cell

Cell surface membranePhotomicrograph

Cheek cell Onion epithelial cell

Cell surface membrane (plasma membrane)

Cell wallCell wall

• Non-living cell wall made of cellulose that encloses the entire plant cell, surrounding the cell membrane.

• The cell wall is fully permeable and is absent in animal cells.

Function:• It protects the cell from injury and gives

the plant cell a fixed shape.

What does a cell consist of?

Cell wall

Only exist in plant cells

Absent in animal cells

What does a cell consist of?

Cell wallPhotomicrograph

Parts of a CellParts of a CellThe protoplasm of a cell is made up of three parts:

Cell surface membrane

• Surrounds the cytoplasm

• Partially permeable

• Hence controls substances entering or leaving the cell

Nucleus

• Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin

• Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

Cytoplasm

• Protoplasm between the cell surface membrane and nucleus

• Where most cell activities occur

• Contains enzymes and specialised structures (organelles)

nucleoplasm nucleolus chromatin nuclear envelope

Cytoplasm

Cytoplasm

Cytoplasm

Cytoplasm

Cheek cell

Drawing of Onion epithelial cell

Parts of a CellParts of a CellThe protoplasm of a cell is made up of three parts:

Cell surface membrane

• Surrounds the cytoplasm

• Partially permeable

• Hence controls substances entering or leaving the cell

Nucleus

• Consists of nucleoplasm, nuclear envelope, one or more nucleoli and chromatin

• Functions: controls cell activities (e.g. cell growth and repair of worn out parts) ; ;essential for cell division. Cells without nucleus cannot divide and have short lifespans.

Cytoplasm

• Protoplasm between the cell surface membrane and nucleus

• Where most cell activities occur

• Contains enzymes and specialised structures (organelles)

nucleoplasm nucleolus chromatin nuclear envelope

Nucleus

Nucleus- what is inside?

Chromatin -A network of thread-like structures in the

nucleus -It controls the activities of the cell, such as

cell division -Each chromatin is made up of proteins and

deoxyribonucleic acid (DNA)

DNA contains: -Hereditary information -Instructions that a cell needs for carrying out

all chemical reactions within itself.

Nucleus- what is inside?

Chromosome - When the cell is dividing, chromatin condenses and becomes highly coiled structures called chromosomes (which appear as thick, rod-shaped structures under light microscope)

chromosome

The Nucleus

Nucleus

The nucleus

Nucleus

Cheek cell Onion epithelial cell

Vacuole

-Fluid-filled space enclosed by a membrane

-Contained in the cytoplasm

Function:-Storage of substances within the cell

Vacuole

Animal Plant

Size and number

Small and many

Large and only one

Contents Water; food substances

Cell sap (contains dissolved substances

such as sugars, mineral salts and amino acids,

enclosed by a membrane called tonoplast)

How long do they exist?

Temporarily More permanent

Vacuole

Vacuole

Vacuole

Chloroplast

-Oval structures found in plant cells-Found in the cytoplasm

Function:

-Contains the green pigment chlorophyll, which is essential for plants to make food (the process of photosynthesis)

The chloroplast

Chloroplast

Only exist in plant cells

Absent in animal cells

Chloroplast

Chloroplasts

Photomicrograph

ChloroplastElectronmicrograph

Mitochondria (sin: Mitochondrion)

-Small, sausage-shaped -Can be seen clearly under electron microscope

Function:- Aerobic respiration occurs in the mitochondria

-Aerobic respiration is the process whereby food substances are oxidised to give energy the cell needs to carry out activities like growth and reproduction

MitochondriaElectronmicrograph of mitochondrion

MitochondriaElectron-micrograph:

MitochondriaElectron-micrograph:

(b) A plant cell

MitochondriaElectronmicrograph:

Ribosome

Small, round structures Either attached to certain membranes in the cells or lie freely in the cytoplasm.

Function: Synthesize proteins in the cell

RibosomesElectron-micrograph:

In summary- Most cells share certain features:

In summary- Most cells share certain features:

CytoplasmProtoplasm

Nucleus Cell surface membrane

Nucleoli- Building proteinsNucleoplasm- small round mass of protoplasm calledthe nucleoplasmNuclear envelope- Separates nuclear content from the surrounding CytoplasmChromatin threads- Found in nucleoplasm, containhereditary materials which condense to form chromosomes

•Partially permeable membrane covering of cell

•Controls substances entering and leaving cell

•Gel-like substanceforming major part of cell•Site where most organelles are found:Mitochondria (sausage shaped) -for cell respirationCentrioles -involved in cell divisionChloroplasts -Contains chlorophyll, green pigment needed forphotosynthesisVacuoles -fluid-filled storage sacsRibosomes- Synthesise proteins

Cell seen under electron microscope

Cell seen under electron microscope

Rough endoplasmic reticulum Rough endoplasmic reticulum • Rough endoplasmic reticulum (RER) has a surface that

appears rough because of small particles called ribosomes that are attached to its outer surface. The outer surface of the RER is continuous with the nuclear envelope.

• Ribosomes are small round structures that are either attached to the membrane of the RER or lie freely in the cytoplasm. They are needed to synthesise proteins.

• The ribosomes attached to the RER make proteins that are usually transported out of the cell

• The ribosomes lying freely in the cytoplasm make proteins that are used within the cytoplasm of that cell.

• The RER transports proteins made to the Golgi apparatus for secretion out of the cell.

Smooth endoplasmic reticulumSmooth endoplasmic reticulum

• The smooth ER (SER) does not have ribosomes attached to its membrane. SER is more tubular that than the RER. It is connected to the RER.

• The SER synthesises fats and steroids and converts harmful substances into harmless materials.

Golgi apparatusGolgi apparatus• Golgi apparatus or Golgi body is shaped like a

disc.• It consists of a stack of flattened spaces

surrounded by membranes. Vesicles or tiny spherical spaces enclosed by a membrane can be seen fusing with one side of the Golgi apparatus and pinching off from the opposite side.

• The Golgi apparatus stores and modifies substances made by the ER and packages these substances in vesicles for secretion out of the cell.

Plant and animal cells: SimilaritiesPlant and animal cells: Similarities

• Both have nuclei

• Both have cell membranes

• Both have cytoplasm

• Both have mitochondria, ribosomes, ER, Golgi apparatus, vesicles

Plant and animal cells: Differences

Plant and animal cells: Differences

Animal cell Plant cell

Many small vacuolesMany small vacuoles

No chloroplastsNo chloroplasts

No cell wallNo cell wall

centrioles presentcentrioles present

No regular shapeNo regular shape

A large central vacuoleA large central vacuole

Chloroplasts presentChloroplasts present

Cellulose cell wallCellulose cell wall

No centriolesNo centrioles

Regular shapeRegular shape

DifferentiationDifferentiation• Growth in an organism involves cell division.• New cells produced may change and develop into new

tissues.• This process by which a cell becomes specialised for a

specific function is called differentiation. Cells may develop special structures or lose certain structures for them to carry out specific functions.

e.g. Human cells become differentiated to form various types of cells:

liver cells, muscle cells, sperm cells, epithelial cells, blood cells, etc

e.g. Plant cells differentiate to form xylem cells, phloem cells, etc

Root Hair CellRoot Hair Cell

Functions Adaptations

Absorption of water & Absorption of water & mineral salts from soilmineral salts from soil

Long and narrow to increase thesurface area: volume ratio,thus water and mineral salts can be efficiently absorbed from the soil.

Surface Area to Volume RatioSurface Area to Volume Ratio

Cube Surface area/cm2

Volume/cm3 Surface area: volume

Side 1 cm

Side 2 cm

Side 3 cm

6 cm2

24 cm2

54 cm2

8 cm3

1 cm3

27 cm32:1

3:1

6:1

Xylem VesselsXylem VesselsFunctions Adaptations

To provide support for To provide support for

stem & leavesstem & leaves Lignin deposited on wall

To conduct water & salts To conduct water & salts from roots to leavesfrom roots to leaves

Long & thin tubes, no cross walls or protoplasm which enables water to move easily through the lumen (central space)

Red Blood CellsRed Blood CellsFunctions Adaptations

To carry oxygen To carry oxygen around the bodyaround the body

-Circular biconcave, increases the SA to Vol. ratio. -no nucleus, enabling it to contain more haemoglobin

A group of cells work together to form a tissue.

intestinal epithelium (tissue) made up of intestinal epithelial cells

epithelium in the trachea (tissue) made up of epithelial

cells and gland cells

cartilage in the trachea (tissue) made up of

connective tissue cells

epithelium in the lungs (tissue) made up of

epithelial cells

connective tissue in the lungs made up of

connective tissue cells

muscle cell

neurones

intestinal epithelial cell

epithelial cell

gland cell

muscle tissue made up of muscle cells

nervous tissue made up of neurones (nerve cells)

connective tissue cell

connective tissue cell

epithelial cell

TissuesTissues

Tissue

A group of similar cells which work together to perform a specific function

-Cells of the same type form simple tissueE.g. epidermis tissue (plants) and epithelial tissues (animals)

-Cells of different types form complex tissueE.g. connective tissue (animals), blood, vascular tissue (plants)

Different tissues combine to form an organ.

trachea (organ)

lungs (organs)

stomach (organ)

intestine (organ)

muscle tissue

cartilage (tissue)

muscle tissue connective tissue

nervous tissue

intestinal epithelium (tissue)

epithelium (tissue)

epithelium (tissue)

Organs Organs

Several organs work together to make up an organ system.

lungs (organs)

trachea (organ)

intestine (organ)

stomach (organ)

digestive system (organ system)

respiratory system (organ system)

SystemsSystems

human (organism)

digestive system (organ system)

respiratory system (organ system)

Various organ systems work together to make up an organism.

Specialised Cells, Tissues, Organs & SystemsSpecialised Cells, Tissues, Organs & Systems

controls cell activities

Protoplasm

Cell surface membrane

TissuesCELL Organs

Cellulose cell wall (found only in plants)

made up of

consists of

whichwhichwhich

Nucleus Cytoplasm

and contains

Chromatin (made up of DNA)

Organism

Organ systems

is the partially permeable, outer covering enclosing the

cytoplasm

surrounds the nucleus and is where most cell activities occur

Chloroplasts (in plant cells)

Mitochondria (sites of energy release)

contains organelles

Vacuoles (contain water and food substances)

Ribosomes (involved in protein synthesis)

You should be able to:You should be able to:• Know the functions and identify from diagram and

photomicrographs, the nucleus, chloroplast, ribosome, mitochondrion, endoplasmic reticulum.

• Examine under the microscope an animal cell (from fresh liver& human check cell) and a plant cell (from Hydrilla & onion ) • Compare and contrast the structures of plant and animal

cell• Relate the adaptations of a cell structure to its functions

for the following: Absorption-root hair cells/ Conduction and support- xylem vessels /Transport of oxygen-red blood cells

• Differentiate between the terms cell, tissues, organ and organ system.