cell structure and

7/28/2019 Cell Structure And

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CHAPTER 2


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Plant Cell


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Animal Cell


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Cell Wall (In plant cells only)

Characteristic

1. Rigid outer layer that surrounds the plasma membrane.

2. Composed of cellulose, a tough and fibrous carbohydrate.3. permeable.

Function

1. Give a shape.

2. Provides mechanical support .

3. Protect the plant cell.

Cellular components of animal and plantcells.


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Vacuole (usually in plant cell)

Characteristic

1. Spherical or oval shaped sac filled with fluid calledtonoplast.

2. Fluid is known as cell sap.

3. In microorganism have contractile vacuoles and food

vacuoles.

Function

1. Store food

2. Regulate water balance in cells.

3. Turgidity of cell give support to plant

4. Contractile vacuoles help regulate amount of water.


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Centrioles (in animal cell only)

characteristic

1. Exist in pair near the nucleus

2. Small cylindrical structure

Function

1. Form spindle fibres during cell division

2. Synthesis cilia and flagella of small organism.

Nucleus

Characteristic

1. Large, dense, spherical organelle enclosed by a nuclear membrane.

2. Contain nucleoplasm , nucleolus and chromatin.

Function

1. Controls all activities of the cell.

2. Synthesis of ribosomes and DNA.


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Mitochondria

Characteristic

1. Cylindrical or oval shaped

Function1. Involved in cellular respiration.

(glucose broken down with help ofenzymes, release energy. The energy

released is store in the form of ATP)

Ribosome

characteristic

1. Spherical organelles2. Consist 2 subunit containing protein and

RNA

Function

1. Synthesis of protein such as enzymes


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Endoplasmic reticulum (ER)

Characteristic

1. Consist of an extensive flattened

membrane folded repeatedly to form alarge network of interconnected tubesand sacs.

2. Rough ERwhich has ribosome on its

surface.3. Smooth ERwhich has no ribosomes.

Function

1. Rough ERtransport proteins made by

ribosome to one part of the cell toanother

2. Smooth ERsynthesis lipids and is thecentre for detoxification of drugs,


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Golgi apparatus

characteristic

1. consist of a stack of f lattened

membrane sacs.Functions

1. As a processing packaging andtransporting centre of carbohydrates,protein, phospholipids andglycoproteins.

Cytoplasm

Characteristic

1. Jelly like mediumFucntion

1. Place where biochemical reactionsoccur


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Lysosomes

Characteristic

1. Spherical

2. Bounded by single membrane

3. Contains hydrolylic enzymes.

Functions

1. Break down complex organic molecules such as proteins,

lipids polysaccharides and nucleic acids.2. Eliminate damage organelles to renew it self.

3. Breaking down the bacterial cell wall.


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Chloroplast (in green plants)

Characteristic

1. Disc shaped structure

2. Contains the green pigment chlorophyll.

Functions

1. Chlorophyll traps sunlight and converts light energy intochemical energy during photosynthesis.


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Comparing the structure of animal and plant cell

Animal cell Similarities Plant cell

Both animal and plant cells have plasma membrane, cytoplasm, nucleus,endoplasmic, reticulum, Golgi apparatus, ribosome, mitochondria.


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Animal cell Different Plant cell

Not fixedShape

Fixed

AbsentCell wall

Present

AbsentVacuoles

Present

If present are smallChloroplast

Has large vacuoles filledwith cell sap

Carbohydrate are storedin the form of glycogen

granulesFood storage

Carbohydrate are storedin the form of starch

grains.

PresentCentriole

absent


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1. Organism which are made up of only cell are calledunicellular organism.

2. Unicellular organism can feed, respire, excrete,move, respond to stimuli, reproduce and grow.

3. Examples of unicellular organism areAmoeba sp,Paramecium sp, Euglena sp, Chlamydomonas sp


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Amoeba sp.

Structure

1. Does not have definite shape2. Enclosed by plasma membrane

3. Cytoplasm is divide into two layers, outer layercalled ectoplasm and inner layer is called

endoplasm.4. Has nucleus.

Habitat1. Freshwater environment such as in lakes andponds.

2. Soil water


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Reproduction

1. Reproduce asexually

2. Binary fission during favourable conditions

3. Formation of spores during unfavourable(environment not conducive) conditions.


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Respiration

Exchanges of respiration gases through the plasma

membrane by diffusion.

Locomotion

1. Moves by extending the pseudopodium to thedirection in wants to move.

2. Pseudopodia is known as false feet


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Feeding

1. Feeds on bacteria, algae and othermicroorganisms.

2. Feeds through phagocytosis process.

3. Pseudopodia extend to surround food, engulf itto form a food vacuole. Then digest the food by a

enzymes called lysozymes.


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Excretion

1. Osmoregulation is carried out by contractile vacuole.

2.Water diffuses into the cell by osmosis and fill thecontractile vacuole.

3. Then contract to expel its content when vacuole isfilled to a maximum size.

Response to stimuli

1. Moves towards favourable stimuli such as food usingpseudopodia.

2. It moves away from unfavourable stimuli such asacidic or alkaline solutions, bright light and hightemperature.


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Cell specialisation in multicellular organism

1. Multicellular organism are organisms which aremade up of more than one cell.

2. Multicellular organisms begin life as a single cell,a zygote which is formed when an ovum isfertilised by a sperm.

3. The zygote divide repeatedly to form identicalcells which form ball of cells known as embryo.

4. The cell of the embryo grow changes shape anddifferentiate to carry out specific function.


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Example is specific function of:

a) White blood cell?

b) Nerve cell?c) Red blood cell?

d) Sperm cell?


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Cell organisation in multicellular organism

1. cell of the same type which carry out a commonfunction are organised into tissue.

2. A tissue is group of similar cells performing aparticular function.

3. Different type of tissue group together to form anorgan.

4. An organ is a group of tissue that performs a

specialised function.5. Several organs are found within a system.

6. All system work together to make up an

organism.


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Cell organisation in animals

Tissue

1. There are 4 main types of tissues in animals;

a) Epithelial tissueb) Muscle tissue

c) Nerve tissue

d) Connective tissue


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a) Epithelial tissue

Consist of one layer or more cell.

Cells of an epithelium tightly interconnected and form

a continuous layer over body surfaces(skin andMouth)and inner linings of cavities(digestive tract andlungs).

Functioni. Epithelial tissue at the outermost layer of the skin

Protect the underlying tissue and organs

Prevents dehydration of the skin

ii. Epithelial tissue at the lining of intestine

Secretes digestive enzymes

Absorb nutrient


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iii. Epithelial tissue at the lining of lung

Allows efficient exchanges of respiratory gases

iv. Epithelial tissue at the lining of trachea

Consist modified structures called cilia.

b) Muscles tissue

1. Most abundant tissue

2. 3 type of tissue;a) Smooth muscle

b) Cardiac tissue

c) Skeletal muscle


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Smooth muscle

Responsible for involuntary body activities such as

the peristaltic movement along digestive tract.

Skeletal muscles

Involved in voluntary movements Contract an relax to move the bones

Cardiac muscle

Contract to pump blood to all parts of the body


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c) Nerves tissue

Composed of neurones or nerve cell.

Neurone consist of a cell body and nerve fibrescalled dendrites and axons.

Functions: To detect stimuli and transmit electrical signals

called nerve impulses to muscle or glands.

Nerve tissue control and coordinates activities ofthe body.


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d) Connective tissue

Type of connective tissue Function

Loose connective tissue Binds epithelia to underlying tissue and holdsorgans in place.

Dense fibrous connectivetissue

1. Connect muscles to bones (tendons)2. Join bones together at join (ligament)

CartilageStrong flexible connectivetissue.

1. Provide support to the nose, ear andcovers the ends of bones at join.

2. Act as cushions to absorb pressure.

Bone Provides protection to organs and support thebody.

Blood cells Has regulating, transporting and protectivefunctions.

Adipose tissueTightly packed cell stores fat.Found in the dermis and

organ.

1. Act as an energy reserve.2. Provide insulation and protection.


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Loose connective tissue

Adipose tissue

Bone tissue Bone tissue Cartilage


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Organs

Formed by two or more tissue Working together to perform particular function

Example of organs include:i. Heart

ii. Skin

iii. Lungs

iv. Kidney

v. Eyes

vi. ears


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Skin

Is a organs because consist of various type of tissuejoined together .

Two main layer ;

epidermis (outer layer made up of epithelial tissue)

dermis (composed of connective, nerve, epithelial andmuscle tissue)

Function Covers the body to protect

Act as barrier against infection, Physical trauma andWater loss.


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System

Consist several organs that work together to perform acommon function.

Consist of 11 system


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Cell organisation in plants

Tissue Two type of tissue

a) Meristematic tissue

b) Permanent tissues

a) Meristematic tissue

1. consist of small cells , thin walls, large nuclei, dense

cytoplasm, no vacuoles.2. Actively dividing cells

3. Located at the tips of roots and buds of shoots.


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b) Permanent tissue

Mature tissue

3 type of permanent tissuei. Epidermal tissue

ii. Ground tissue

iii. Vascular tissue

i. Epidermal tissue

Outermost layer covers the stem, leaves, and root of

young plant. Flat and large vacuoles

Covered waxy waterproof called cuticle.


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Function of cuticle?

1

2 3

Root epidermal cells have long projection called roothair to increase the surface area for water absorption.

Guard cell found among epidermal cell to control theopening and closing of stomata.

Guard cell containing chloroplast.


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ii. Ground tissue consist of parenchyma tissue,collenchyma tissue and sclerenchyma tissue.

Parenchyma tissue

Found in organs of plant

Thin primary wall

Large vacuoles

Function

Store sugar and starch.

Give support and shape to plant


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Collenchyma tissue

Thickened cell wall

Function Support non woody plant, young stem and petioles

Sclerenchyma tissue

Have cell wall

Thickened by lignin.

Function Give support and

mechanical strength to mature regions of a plant


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iii. Vascular tissue.

Consist of Xylem and Phloem

Xylem

Consist mainly of xylem vessels joined together end toend.

Consist cytoplasm

Function

Transport of water and dissolved minerals salts fromthe roots to other part of the plant.

Provide support and mechanical strength to the plant.


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Phloem

Consist mainly of sieve tubes.

Arranged end to end to form long continuous tube-like structure.

Function

Transport organic compounds such as carbohydrateand amino acids to other part of the plant.


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Organs and systems in plant


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Flowering plant consist of root system and shoot

system.

Root system consist of all the root of a plant.

Shoot system consist of stems, leaves, buds, flowers,

and fruit.

stem and branches act as a support system for the

plant.


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Regulating the internal environment

The internal environment of multicellular organism

1. Intercellular space between cells is filled with a fluidcalled the interstitial fluid.

2.The interstitial fluid forms the internal environmentof an organism.

3. The internal environment is the environment withinthe body of an organism.

4. The cells obtain the substance required forbiochemical reactions from the interstitial fluid.

The necessity for maintaining an optimal internal


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The necessity for maintaining an optimal internalenvironment.

1. The physical and chemical factors of the internalenvironment must be maintained regardless of theconditions outside of the cell in order for cell to functionoptimally

1. Physical factors :a) Temperature

b) Blood pressure

c) osmotic pressure

2. Chemical factors:

a) Salt

b) Sugar content

c) pH value


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Homeostatis

The maintenance of a relatively constant internalenvironment for the cells to function optimally.

Eg; metabolism of the body is affected by the changesin the chemical factors and physical factors.

Glucose and oxygen, temperature and osmoticpressure.

These changes are regulated by the homeostaticmechanisms which maintain the internal environmentso that the metabolic process can proceed at optimumrates.


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Any increase or decrease will trigger the homeostasismechanism to raise it back to normal.

The mechanism that govern homeostasis is called thenegative feedback mechanism.

Th i l t f i t i i t i i


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Normalcondition

Control centreReceptor Effector

Receptor Control centre Effector

Normalcondition

Factor value

increase

Negative

feedback

mechanism

Negative

feedback

mechanism

Factor value

increase

The involvement of various system in maintaining anoptimal internal environment

l b d


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Example; body temperature

Is regulated by the integumentary system, nervoussystem, circulatory system, muscular system, and

endocrine system.

When the temperature rises above the normal level,

the receptors in the skin detect the changes. This information is transmitted to hypothalamus at

the centre in the brain.

The hypothalamus activated blood vessels and sweatglands. The blood vessels dilate and allow more bloodto flow near the surface of the body


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This will increase heat loss to the externalenvironment.

The sweat glands are activated by the nervous systemto produce more sweat that will lower the bodytemperature through evaporation.

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