FOLIO: biology form 4 chapter 2: Cell structure and organisation

8/8/2019 FOLIO: biology form 4 chapter 2: Cell structure and organisation

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Introduction

Cell are the fundamental units of all living things. All living organisms are made up of

one or aggregates of cells. Cells arise only via division of previously existing cell. The

common components of all cells are plasma membrane, cytoplasm, and genetic material.

In selecting this project, the study team has taken the following consideration:

1. Cell structure

a) Draw and label an animal cell

b) Draw and label a plant cell

c) Identifying the cellular components of an animal cell

d) Identifying the cellular components of a plant celle) Stating the functions of the cellular components of an animal cell

f) Stating the functions of the cellular components of a plant cell

g) Comparing and contrasting an animal cell and a plant cell

2. Cell organisation

a) Stating why cell specialization is necessary in multicellular organisms but not in

unicellular organisms

b) Describing cell specialisation in multicellular organisms

c) Describing cell organisation in the formation of tissues, organs and systems in

humans, animals and plants

d) Stating the meaning of internal environment

e) Identifying the factors affecting the internal environment

f) Explaining the necessity to maintain optimum environment

g) Describe the involvement of various systems in maintaining optimal internal

environment

3. Appreciating the Uniqueness of the Cell

a) Predicting the state of state of a cell if any cellular component is missing

b) Illustrating that most cells are specialised for the function that they perform

As an initial step, discussion among the group members were held where several

prospective projects were discuss to ensure a better understanding of the project,

nevertheless to become it a success.

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2.1 Cell Structure

2.1.1 Cross Section of Plant Cell and Animal Cell

a) Plant Cell

Plant cells are made up of many organelle:

- Plasma membrane

- Cell wall

- Nucleus

- Mitochondria

- Ribosome

- Endoplasmic Reticulum

- Golgi Apparatus

- Cytoplasm

- Vacoule

- Lysosome

- Chloroplast

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b) Animal Cell

Animal cells are mede up of many organelle:

- Plasma membrane

- Nucleus- Mitochondria

- Ribosome

- Endoplasmic Reticulum

- Golgi Apparatus

- Cytoplasm

- Vacoule

- Lysosome

- Centriole

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2.1.2 Organelle That Contain In Plant Cell And Animal Cell

Planat Cell Organelle Animal Cell

Present Cell Wall Absent

Present Chloroplast Absent

Absent Centriole Present

Usually a large central

vacuole, contains cell sap

Vacuole Usually small and

numerous, filled with water

or food

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2.1.3 Structure of Cellular Components

a) Plasma Membrane

- Also known as cell membrane

- Thin, elastic and semi permeable

- It is composed of proteins and phospholipids

b) Cell Wall

- Outer layer of plant cells that is made up of cellulose fibres

- This layer provides strength to the cell

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c) Nucleus

- A spherical organelle with a nuclear membrane, nucleolus and nucleoplasm that

cointains chromosomes

- It may cointain one or more spherical bodies called nucleolus

- It is found in all cells, except red blood cells and seive tubes of phleom

d) Mitochondria

- Usually they are spherical, oval or sausage shaped

- Mitochondria have 2 layer of membrane. The outer membrane is smooth and the inner

is folded

- It cointains a matrix with a few ribosomes, a circular DNA molecule and phosphategranules


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e) Ribosome

- They are non membrane bound particles

- An assembly of a big and small sub unit

- Both of subunits are seen as solid spherical granules

f) Endoplasmic Reticulum

- There are 2 types of endoplamic reticulum: rough ER, coated with ribosomes, and

smooth ER, without ribosomes

- A system of flattened, membrane bounded sacs called cisternae in the forms of tubes

and sheets

- A maze of folded sheets and interlocking channels


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g) Golgi Apparatus

- A membrane bound structure with a single membrane

- It is actually a stack of membrane bound vesicles that pack macromolecules for

transport elsewhere in the cell

h) Cytoplasm

- It is jelly like substance that fills the cell

- Cytoplasm is the entire region between the nucleus and the plasma membrane- It consists of about 70% to 90% water, organelles, food reserves, proteins and other

chemical compounds.


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i) Vacuole

- Vacuole are sacs with lipoprotein membrane, usually spherical in shape

- The membrane is called tonoplast

- A vacuole is filled with sugar solution, organic acids, enzymes and pigments.

j) Lysosome

- Lysosomes are roughly spherical bodies bounded by a single membrane and cointain

enzymes

- They are produced bt the Golgi Apparatus

- They cointain digestive enzymes.

k) Chloroplast

- Chloroplasts are found in the green parts of the plants, especially in mesophyll cells of

leaves

- The organelles cointain chlorophyll. They have the shape of biconvex disc bounded by

2 layer of membrane

- Their locationin cells are not fixed, they can move and orientate their larger surface to

the sunlight.

l) Centriole

- Consist of a pair of short hollow cylinders at right angles to each other

- It is usually found in near the nucleus of an animal cell

- It can be found in most animal cell but only appear in the lower plant cells.


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2.1.4 Comparison Between An Animal Cell And Plant Cell

SIMILARITIES

Both has plasma membrane, nucleus, mitochondria, ribosome, endoplasmic reticulum, golgiaparatus, lysosome, and vacoule.

DIFFERENCES

PLANT CELL CHARACTERISTICS ANIMAL CELL

Autotrophic nutrition Type Of Nutrition Heterotrophic nutrition

Bigger Size smaller

Regular shape Shape Irregular shape

Cell wall is made up of

cellulose that provides

stability and rigidity to the

cells

Cell Wall No cell wall

Rarely mobile Movement Often able to move about

(mobile)

Chloroplasts usually present Chloroplast No chloroplast

Large sap vacuole in the

centre of cell

Vacuole No large sap vacuole, if

present is very small

Food storage in the form of

starch grains

Storage Granule Food storage in the form of

glycogen granules

2.2 Functions of Cellular Components

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An organelle is a specialized subunit within a cell that has a specific function, and is

usually separately enclosed within its own lipid bilayer. Within cells there is a network

of organelles that all have unique functions. These organelles allow the cell to function

properly.

2.2.1 Plasma Membrane

The plasma membrane is a very important structure which functions to allow

certain substances to enter or leave the cell by:

a) Transport substance into the cell against the concentration gradient or

pump substances out of the cell.

b) Occur passively without the cell needing to expend any energy to make

them happen which is also known called as "passive transport

processes".

c) Require energy from the cell's reserves to generate carrier protein.

These processes are called "active transport processes".

Diagram: Simple lipid bilayer of plasma membrane

Source: runningstrong-biologylibrary.blogspot.com

Functions of lipid bilayer are:

a) the barrier that keeps ions,proteins and other molecules where they are

needed and prevents them from diffusing into areas where they should

not be.

b) allows cells to regulate salt concentrations and pH by pumping ions

across their membranes

2.2.2 Cell Wall

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The cell wall is a structure that is present in plant cells which surrounds the cell

membrane. This is a special characteristic feature which helps distinguish plant

cells from animal cells that normally act as :

a) Maintaining the shape of the plant cell.

b) Support and mechanical strength that allows plants to get tall, hold out

thin leaves to obtain light.

c) Prevents the cell membrane from bursting in a hypotonic medium.

d) Controls the rate and direction of cell growth and regulates cell volume.

e) Tubes for long-distance transport.

f) Cutinized walls prevent water loss.

2.2.3 Nucleus

Diagram: Nucleus structure

Source: electronic.districsides.com

The nucleus regulates all cell activity by controlling the enzymes present. The

chromatin is composed of DNA that contains the information for the

production of proteins. The major functions are:

a) It is involved in cell division.

b) It stores all the information that is to be transferred to the next

generation.

c) Assembly of ribosomes takes place in the nucleolus present inside the

nucleus.

d) DNA replication and transcription processes take place inside the

nucleus.2.2.4 Mitochondria

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The mitochondria provides energy for the cell. They are known as the

powerhouse of the cell because they provide the location for the production of

ATP (adenosine tri-phosphate). ATP is produced by aerobic respiration such as

glycolysis, the Krebs cycle and electron transport. ATP in turn provides energy

for the cell at the molecular level. They gave a role such as:

a) supplying cellular energy as it site for aerobic respiration.

b) signaling, cellular differentiation, cell death, as well as the control of

the cell cycle and cell growth

2.2.5 Ribosome

Ribosomes are cytoplasmic granules composed of RNA and protein, at which

protein synthesis takes place. The function of ribosomes is to:

a) Make proteins in a process called protein synthesis.

b) Help the nucleus down particles in the nucleolus and it is a form of

excrement from the endoplasmic retina and you must have ribosomes to

live.

c) Ribosome turns RNA (Ribonucleic acid) into protein.

d) Storage space for energy.

e) the structural support, and the catalyst for protein synthesis.

2.2.6 Endoplasmic Reticulum

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Diagram: Structure of endoplasmic reticulum

Source: biologycorner.com

The functions of the endoplasmic reticulum vary greatly depending on the

exact type of endoplasmic reticulum and the type of cell in which it resides.

The two common varieties are called rough endoplasmic reticulum and smooth

endoplasmic reticulum.

a) Rough endoplasmic reticulum

I. Providing an internal structural skeleton to support the cell's

shape.

II. Storage of the synthesised materials and minerals.

III. Forming an internal network through which materials can be

transported.

IV. Providing a large surface area.

b) Smooth endoplasmic reticulum

I. Packages proteins for transport.

II. Synthesizes membrane phosolipids.III. Releases calcium.

2.2.7 Golgi Apparatus

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The Golgi apparatus is an organelle found in most eukaryotic cells. The Golgi

apparatus processes and packagesproteins and lipids, after their synthesis and

before they make their way to their destination; it is particularly important in

the processing of proteins forsecretion. Their functions are to collect, pakage

and distribute the molecules made in the cell and used elsewhere by:

a) Separates proteins according to their destinations.

b) Modifies proteins (adds sugar and makes glycoproteins).

c) Packages materials into vesicles which are exported outside the cell.

2.2.8 Cytoplasm

Cytoplasm is a homogeneous, generally clear jelly-like material that fills cells.

The cytoplasm consists ofcytosol and the cellular organelles, except the

nucleus. The cytosol is made up of water, salts and organic molecules and

many enzymes that catalyze reactions. The cytoplasm is the site where most

cellular activities are done. All the functions for cell expansion, growth and

replication are carried out in the cytoplasm of the cell. Functions as:

a) site of many cellular reactions Cytoplasm offers support to the cell.

b) allows the cell to take up 3-dimensional space and the cell's many

organelles to "float" freely throughout.

c) acts as a medium for transport inside the cell.

2.2.9 Vacuole

The vacuole is an important organelle present in the cells of plants, animals,

protists, fungi and bacteria. These cell organelles contain water and different

organic/inorganic molecules. The vacuoles also contain enzymes. Mainly the

roles are:

a) Isolating materials that might be harmful to the cell

b) Containment of waste products

c) Maintaining internal hydrostatic pressure or turgor within the cell

d) Maintaining an acidic internal pH

e) Exporting unwanted substances from the cell.

2.2.10 Lysosome

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Lysosomes are membrane-enclosed organelles that contain an array of enzymes

capable of breaking down all types of biological polymers. Lysossome

functions as:

a) the digestive system of the cell.

b) destroy worn-out or damaged organelles.

c) engulf foreign invaders.

2.2.11 Chloraplast

Chloroplast are those sub-units in a plant cell, which produce food for a plant

through the process of photosynthesis. Chloroplasts are somewhat similar to

mitochondria, a single celled organisms which can produce energy. Functions

as:

a) strores chlorphyll.

b) conduct photosynthesis.

c) capture light energy which causes photolysis of water to conserve free

energy in the form of glucose which the plant uses for food.

2.2.12 Centriole

Centrioles line up the chromosomes inside the cell and then they pull the

chromosomes apart during cell replication. Centriole is a structure found in

eukaryotic animal cells. Plant cells and fungi do no contain centrioles.

Centriole is the part of the cell, which acts as the center for producing

microtubules, which are the component of cytoskeleton which is the skeleton

of the cell that provides both shape and structure to a cell. Act in the cell as:

a) organizing center for microtubules.

b) elps in the organization of Mitotic spindle fibers and in the completion

of Cytokinesis.

2.3 Cell Organisation

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In this sub-chapter, we will learn that although a unicellular organism is made up of

only a single cell, it can perform all the living process just like any other

multicellular organisms.

1. A variety of organisms are made up of only one cell. They are called unicellular

organisms.

Examples of unicellular organisms :

2. Unicellular organisms feed, grow, move, respond to stimuli, respire, excrete and

reproduce. These characteristics are similar to multicellular organisms which are

made up of more than one cell.

3. Unicellular organisms have little problem acquiring and utilizing the natural

resources freely available on earth. But they have to be tiny, and the external

environment they are in would have to be favourable to their needs.

4. In addition to the small size of the cell, another useful strategy to efficiently use to

natural resources to fulfil the needs of the cells would be for an organism to

become bigger and to have specialized structures that do specialized functions.

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For example, we have mouth, stomach, nose, lungs and so on ; plants have roots,

stems, leaves and so on.

5. Since cells should not be big, the organism would have to consist of many cells.

Thus, multicellular organism evolved and it is in itself a strategy to efficiently use

the natural resources to fulfil the needs of the cells.

2.3.1 Living processes of unicellular organisms

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1. Unicellular organism are single-celled organisms that are capable of carrying out

all basic life processes such as nutrition, respiration, excretion, reproduction,

locomotion, growth and response to stimuli.

2. Protozoans like Paramecium sp. and Amoeba sp. are unicellular organisms.

Diagram: Amoeba sp.

3. The Amoeba sp. is a unicellular, aquatic organism that does not have a definite

shape. It is about 0.25 mm in length and is barely visible to the naked eye.

4. It is a mass of protoplasm surrounded by the plasma membrane. The protoplasm

consists of the cytoplasm and an oval-shaped nucleus. The cytoplasm is made up of

an outer, firmerectoplasm and an inner, more watery endoplasm. Food vacuoles

and contractile vacuoles are found in the cytoplasm.

5. Feeding

(a) the Amoeba sp. feeds on bacteria, algae and other microorganisms.

(b) it extends its pseudopodia to surround the food, engulfing them with a drop of

water to form a food vacuole. This is called phagocytosis.

(c) it then secretes enzymes into the food vacuole to digest the food.

(d) the digested food is absorbed into the cytoplasm while the undigested materials

are expelled.

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6. Respiration

The Amoeba sp. respires when oxygen in the water diffuses into the cytoplasm and

the carbon dioxide produced diffuses out into the water.

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7. Locomotion

(a) the Amoeba sp. moves by extending its pseudopodia out towards the direction it

wants to move.

(b) the pseudopodium is formed when the endoplasm flows into the ectoplasm.

(c) the pseudopodia are also known as false feet

(d) the Amoeba sp. can extend a few pseudopodia out at one time. It withdraws the

pseudopodium that does not carry it towards the direction it intends to go.

(e) the irregular extension of the pseudopodia gives the Amoeba sp. its irregular

shape. This type of movement is called the amoeboid movement.

8. Reproduction

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(a) the Amoeba sp. reproduces by binary fission.

(b) when the Amoeba sp. reaches its maximum size, the nucleus divides into two,

followed by the cytoplasm, to form the new daughter cells.

(c) the Amoeba sp. does not reproduce sexually.

9. The Amoeba sp. forms spores when conditions are unfavourable, for example,

when the condition is dry and there is insufficient food. The spores germinate when

conditions become favourable again.

10. The Amoeba sp. regulates the amount of water in the cytoplasm with its

contractile vacuole. The contractile vacuole contracts to expel excess water from

its cytoplasm.

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2.3.2 Cell specialization in multicellular organisms

1. A good strategy to fulfil the needs of constituent cells in a multicellular organism

is to have cells that specialise in carrying out specific functions.

2. In a plant, mesophyll cells found in the leaves are specialised in carrying out

photosynthesis, whereas epidermal cells are for protection of other cells.

3. The function of an individual cell in an organism is not really significant. For

example, contraction of a single muscle cell is not able to cause significant

movement.

4. Cells work in groups. Each group of cells depend on other groups to work. For

example, skeletal muscles depend on information coming from nerve cells before

they can contract. This is known as division of labour.

5. This means that the cells have to be well organised in an organism in terms of

structure and function as well as in terms of interaction amongst the various types

of cells.

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Cells FunctionsCells that cover the whole body Protect the body

Red blood cells Transport oxygen

Muscle cells Contract and produce movement

and/or create force

Cells in the retina of the eyes Recognise external and internal

stimuli

Nerve cells in the brain Conduct nerve impulses


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2.3.3 Cell organisation in a multicellular organism

1. A good strategy to solve the problem of meeting the cells needs is for the organism

to have specialised structures formed into system. For example, we have :

(a) a digestive system to bring in nutrients from the environment.

(b) a respiratory system to bring in oxygen and get rid of carbon dioxide.

(c) a circulatory system to supply the requirements to each cell.

2. In each system, there are specialised organs that carry out more specific functions.

For example, in the respiratory system we have the nose, the respiratory tract and

the lungs.

3. Each of the organs consists of tissues. A tissue is a group of cells that perform

similar specialised functions. For example, the nose consists of epithelial tissue,

connective tissue, muscle tissue and nerve tissue.

4. In short, besides carrying out general functions like transporting substances across

the cell membrane, breaking down fuel molecules to obtain energy and synthesising

proteins, cells in organism are specialised to carry out specific functions. They are

organised into tissues,organs and organ systems.

5. The hierarchy of cellular organization is :

Cells Tissues Organs Organ systems Multicellular organism

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Organisation of animal cells into tissues

1. A group of cells that have similar structures and perform similar functions form

tissues.

2. Animal tissues can be divided into four types, namely epithelial, connective,muscle and nerve tissues.

3. The skin is basically made up of three layers :

(a) the outermost layer is the epidermis. This layer consists of epithelial tissue.

(b) the middle layer is the dermis, consisting of connective tissue, nerve tissue and

blood capillaries.

(c) underneath the dermis is the hypodermis, containing muscle tissues and

connective tissue.

Diagram: Cross-section of skin

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Epithelial tissue

1. Epithelial tissue consists of cells closely packed to form one layer or several layers

lining the outer body surface. For example, the skin, mouth cavity and nasal cavity.

2. It also covers the outer and inner surfaces of organs such as the digestive tract,

trachea, blood vessels, oesphagus and lungs.

3. Some are specialised to form glandular tissues, for example sweat glands in the

skin and exocrine glands (the glands that secrete substances such as enzymes via

ducts) in the digestive tract.

4. The function of epithelial tissue depends on its locaton in an organ.

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Connective tissue

1. Connective tissue is made up of a variety of cells embedded in a large amount of

intercellular substance called matrix.

2. The matrix could be in the form of

(a) liquid, for example the plasma of the blood

(b) soft solid, for example the chondrin of the cartilage.

(c) hard solid, for example the inorganic matrix of the bone

3. Connective tissues are the most varied in terms of structure and function.

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Muscle tissue

1. Muscle tissue consists of cells that are able to contract and produce motion.2. The three types of muscles are smooth muscle, cardiac muscle and skeletal

muscle.

Types of muscle tissues :

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Types of connective

tissue

Description Function

Loose connective

tissue

Found in the spaces

between organs

Holds the organs

togetherFibrous connective

tissue

Forms tendons and

ligaments

Tendons : Connect

bones to muscles.

Ligaments : Connect

bones to bones

Adipose tissue - Stores fat

Bones Form the skeleton Protect the organs,

involved in body

movementBlood Consists of two

major cell types

Red blood cell :

carries oxygen

White blood cell :

involved in

community

Cartilage Forms smooth and

flexible surfaces

Between bones : acts

like cushion. In the

nose and ear : forms

the shape of the

organs.


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3. Skeletal muscle is called voluntary muscle because it is under

voluntary(conscious) control, whereas smooth muscle and cardiac muscle are

involuntary muscles.

4. Contraction of the cardiac muscle that produces heartbeat and contraction of the

smooth muscle of the blood vessels that controls of the blood pressure occur every

second of your life without your conscious control.

5. It is impossible for us to control the blood pressure consciously every second of

our lives. That is why it is under involuntary control.

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Nerve tissue

1. Nerve tissue consists of cells called neurons.

2. These cells are specialised in transmitting nerve impulses.

Diagram: Nerve tissues

Organisation of animal tissues into organs

1. A group of different tissues that work together to carry out a specific function

form an organ. For example, the heart is an organ that consists of :

(a) muscle tissue(cardiac muscle) that contracts and causes the pumping action of

the heart.

(b) epithelial tissue that lines the inner and outer surfaces of the heart

(c) connective tissue that makes the heart elastic and strengthens the heart walls and

valves.

(d) nerve tissue that regulates the heart rhythm and controls the strength of

contractions of the heart.

2. Other organs like the skin, stomach, lungs, kidneys, intestine, liver, blood vesselsand so on are also formed from tissues.

Organisation of animal organs into systems

1. An organ system consists of a group of organs that work together to produce major

functions like respiration, digestion, excretion and circulation. There are 11 major

organ system in a human body.

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2.3.4 Organ Systems and their functions

I. Integumentary System

Functions to protects against environmental hazards; helps control body

temperature. Composed of skin and derivates.

II. Skeletal System (206 bones)

Functions to provides support; protects tissues; stores minerals; forms blood

Composed of bones, cartilages, and Joints

III. Muscular System (600 muscles)

Functions to produces movement and locomotion; provides support; generates heat

Skeletal Muscle striated, multinucleated, voluntary attached to the skeleton by

Tendon

IV. Nervous System

Functions to control body movements and functions; memory; and monitors internal

and external environment.

Directs immediate response to stimuli, usually by coordinating the activities of other

organ systems

Composed of brain, spinal cord, and nerves

V. Endocrine System

Functions to control body functions through chemical messengers called hormones

Directs long term changes in other organs

VI. Lymphic System

Function to defend the body against infection and disease; returns tissue fluid to the

blood stream

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VII. Cardiovascular System

Functions to transports dissolved materials, including nutrients, wastes and gases and

to protect the body from infections

Contains the heart, blood vessels, and blood

VIII. Respiratory System

Functions to Delivers air to sites where gas exchange can occur between the air and

circulating blood

IX. Digestive System

Functions to process food; absorbs nutrients; eliminates waste products

Chemical digestion (breaking chemical bonds) and mechanical digestion (breaking

large pieces into small pieces)

X. Urinary System

Functions to Eliminates excess water, salts and waste products

XI. Reproductive System

Functions to pass genetic information on to the next generation. Development of

gametes, sexual characteristics, development of offspring, and care for offspring.

Separated into male and female.

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Diagram: The human body system

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Permanent tissue

1. Permanent tissues are differentiated tissues. They can be divided into epidermal

tissue, groundtissue and vascular tissue.

2. Epidermal tissue consists ofspecialised parenchyma cells. It is analogous to the

epithelial tissue in animals.

3. The epidermal tissue covers the outer surfaces of leaves, stems and roots,

protecting the underlying tissues.

4. In the leaves, the epidermal cells secrete a waxy layer called cuticle, which

reduces loss of water via transpiration.

5. A few epidermal cells on the leaves are modified to form guard cells that can

open and close stomata.

Diagram: Guard cell

6. In the roots, the epidermal cells are modified to form root hairs.

Diagram: Root hair

7. Vascular tissues are those involved in transport of water and other substances

from the roots to the leaves and vice versa.

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8. The vascular tissues form continuous vessels in all parts of a plant and can be

divided into xylem and phloem.

Diagram: Xylem and phloem

9. Xylem, a hollow tube is formed from elongated dead cell walls that connect to one

another end to end from the roots to the leaves. The function of xylem is to

transport water and mineral salts from the roots up to the leaves via capillary

action, facilitated by transpiration.

10. Phloem consists of elongated, living cells that connect end to end from a cell to

another forming a tube. Its function is to transport nutrients from the leaves to

other parts of the plant.

11. Besides transporting water and nutrients, the vascular tissue also provides

strength to the stem and branches of a plant.

12. Cells other than those in the epidermal, vascular and meristematic tissues belong

to the ground tissues.

13. Ground tissue fills up to the spaces between the epidermal and vascular tissues,

just like little pieces of polystyrene filling up the spaces between glass materials in

a box.

14. Some of the cells carry out photosynthesis, some store food materials and some

provide strength to plants.

15. Once matured, some cells of the ground tissue die and some remain alive. The

cell walls of the dead cells provide support and strength to the plant.

16. The ground tissue consists of parenchyma, chollenchyma and sclerenchyma cells.

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Diagram: The ground tissue

17. Unlike animals, plants do not have very distinct organs and organ systems. Plant

organs include roots, stems and leaves, all of which consist of all types of tissue.

Systems in plants include circulatory, reproductive and photosynthetic systems.

The nature of the cellular enviroments in plants and in animals

1. The intercellular space in plants is filled with air, whereas the intercellular space in

animals is filled with liquid.

2. The extracellular fluid is the internal environment of animal.

3. The extracellular fluid of animals consists of interstitial fluid, blood plasma

and otherbody fluids that stay outside the cell.

4. Since the cells get the substances required to run the biochemical reactions from

the internal environment, the chemical parameters such as blood glucose level,

concentration of oxygen and carbon dioxide in the bloodstream, waste product and

pH of the internal environment must be regulated so that they always meet the

requirement of the cells.

5. Since the biochemical reactions depend on the physical parameters such as body

temperature and blood pressure, they must also be regulated.

6. The chemical and physical parameters of the internal environment are regulated

via a process called homeostasis.

7. Thus, homeostasis is a process that regulates the chemical and physical parameters

in the internal environment so that the conditions are always suitable to meet the

needs of the cells.

2.3.6 Regulation of the internal environment in human beings and animals

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1. Regulation of chemical and physical parameters in the internal environment is

quite complex.

2. It involves all the organ systems, including the respiratory system, the circulatory

system, the excretory system, the nervous system, the endocrine system and the

muscular system.

Systems involved in maintaining optimal internal environment :

Parameter System that control

Blood glucose level Endocrine, circulatory and

digestive systems

Concentration of oxygen

and carbon dioxide in the

bloodstream

Respiratory, circulatory and

nervous systems

pH Respiratory, circulatory and

excretory systems

Body temperature Nervous, circulatory,

endocrine, muscular and

integumentary systems

Blood pressure Endocrine, nervous,

excretory and circulatory

systems

Waste product (urea) Excretory, circulatory,

nervous and endocrine

systems.

2.4 The Uniqueness of the Cell

2.4.1 Unique properties of stem cells

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Stem cells differ from other kinds of cells in the body. All stem cellsregardless of

their sourcehave three general properties: they are capable ofdividing and renewing

themselves for long periods; they are unspecialized; and they can give rise to

specialized cell types. Stem cells are capable of dividing and renewing themselves for

long periods. Unlike muscle cells, blood cells, or nerve cells, which do not normally

replicate themselves. Stem cells may replicate many times, orproliferate. A starting

population of stem cells that proliferates for many months in the laboratory can yield

millions of cells. If the resulting cells continue to be unspecialized, like the parent stem

cells, the cells are said to be capable of long term self-renewable.

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Diagram:Long-term self-renewal

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Scientists are trying to understand two fundamental properties of stem cells that relate to their

long-term self-renewal:

1. Why can embryonic stem cells proliferate for a year or more in the laboratory without

differentiating, but most non-embryonic stem cells cannot

2. What are the factors in living organisms that normally regulate stem cell proliferation and self-

renewal?

Discovering the answers to these questions may make it possible to understand how cell

proliferation is regulated during normal embryonic development or during the abnormal cell

division that leads to cancer. Such information would also enable scientists to grow

embryonic and non-embryonic stem cells more efficiently in the laboratory.

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Diagram:Embryonic stem cellsproliferate
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The specific factors and conditions that allow stem cells to remain unspecialized are of great

interest to scientists.

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It has taken scientists many years of trial and error to learn to derive and maintain stem cells in

the laboratory without them spontaneously differentiating into specific cell types. For

example, it took two decades to learn how to grow human embryonic stem cells in the

laboratory following the development of conditions for growing mouse stem cells. Therefore,

understanding the signals in a mature organism that cause a stem cell population to proliferate

and remain unspecialized until the cells are needed. Such information is critical for scientists

to be able to grow large numbers of unspecialized stem cells in the laboratory for further

experimentation.

Stem cells are unspecialized. One of the fundamental properties of a stem cell is that it does

not have any tissue-specific structures that allow it to perform specialized functions. For

example, a stem cell cannot work with its neighbors to pump blood through the body (like a

heart muscle cell), and it cannot carry oxygen molecules through the bloodstream (like a red

blood cell). However, unspecialized stem cells can give rise to specialized cells, including

heart muscle cells, blood cells, or nerve cells.

Stem cells can give rise to specialized cells. When unspecialized stem cells give rise to

specialized cells, the process is called differentiation. While differentiating, the cell usually

goes through several stages, becoming more specialized at each step.

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Scientists are just beginning to understand the signals inside and outside cells that trigger each

stem of the differentiation process. The internal signals are controlled by a cell's genes, which

are interspersed across long strands of DNA, and carry coded instructions for all cellular

structures and functions. The external signals for cell differentiation include chemicals

secreted by other cells, physical contact with neighboring cells, and certain molecules in the

microenvironment. The interaction of signals during differentiation causes the cell's DNA to

acquire epigenetic marks that restrict DNA expression in the cell and can be passed on through

cell division.

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Many questions about stem cell differentiation remain. For example, are the internal and

external signals for cell differentiation similar for all kinds of stem cells? Can specific sets of

signals be identified that promote differentiation into specific cell types? Addressing these

questions may lead scientists to find new ways to control stem cell differentiation in the

laboratory, thereby growing cells or tissues that can be used for

Diagram: Specific purposes such as cell-based therapies or drug screening.

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Conclusion

After going through the project, it can be conclude that there are basic skills, and

guidelines to follow for biological drawings. Some basics of microscopy include light

microscope, magnification, electron microscope, electron micrograph, and magnification.

Cellular structures of cells include plasma membrane, cell wall, cytoplasm, nucleus,

nucleolus, chromosomes, nucleoplasm, nuclear membrane, rough endoplasmic reticulum,

smooth endoplasmic reticulum, Golgi apparatus (body), mitochondrion, and endoplasmic

reticulum.

Similarities between animal and plant cells are nucleus, cytoplasm, cell membrane,

ribosome, Golgi apparatus, mitochondria and endosplasmic reticulum. Differences between

animal cells and plant cells are : size, shape, cell wall, types of vacuole, tonoplast, centriole,

carbohydrate storage and lysosome.

Organelles are little organs performing specialised functions. Types of organelles are

nucleus, endoplasmic reticulum, mitochondria, Golgi apparatus, lysosomes, ribosomes,

chloroplasts, centrioles and vacuoles. Density of organelles is equal to the total number of a

particular organelle per cell. The density of a particular organelle increases to support the

particular specialised function of the cell. The density of mitochondria is high in active cell

such as in : sperm cells, flight muscle cells, meristemic cells, liver cells and kidney cells. The

density of chloroplast is high in palisade mesophyll cells.

The living processes of unicellular organisms are : feeding, locomotion, reproduction,

sensitivity, respiration, growth, excretion, and osmoregulation. Characteristics of the living

processes of Amoeba are locomotion (move using pseudopodium), feeding (phagocytosis,

form food vacuole), reproduction (binary fission, spores), sensitivity (whole cell), growth

(limited by surface/volume ratio), respiration (simple diffusion), excretion (diffusion),

osmoregulation (contractile vacuole). The characteristics of living processes of Paramecium

are quite similar to Amoeba, except that : Paramecium swims with cilia, has a more advanced

mouth part for taking in food , can reproduce sexually by conjugation, and has an anal pore.

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A multicellular organism has more cells, and its size is bigger. When an organism grows

bigger, its life processes also increase in quality and complexity specialisation of cell

functions helps in overcoming this problem. Advantages of specialisation in multicellular

organisms : adapt easily and live in a wider range of environment, allows for increase in size,

gives a wider range of food, have complex bodies and have easy access to other

environmental resources.

The five levels of cell organization from simple to complex of multicellular organisms are

cells tissues organ systems organism. Tissues is a collection of cells of similar

structure and function. An organ consists of two of more types of tissues performing a

specific activitiy. A system consists of two or more organ performing a specific function. An

organism refers to all the organ system within a living thing. The twelve human organ

systems are : skeletal, circulatory, muscular, nervous, digestive, endocrine, sensory,

respiratory, integumentary, lymphatic, reproductive and excretory.

The tissues fluid is an organisms internal environment. The factors affecting the internal

environment are : temperature, pH, osmotic pressure and glucose level. It is necessary to

maintain an optimal internal environment be cause life can only tolerate a limited range in the

fluctuations of temperature pH, osmotic pressure and glucose level. Homeostasis is the

maintenance of this constant internal environment. Organ systems involved in the

maintenance of optimal internal environment are :

a) Temperature circulatory, integumentary, and skeletal systems

b) Osmotic pressure nervous and endocrine systems

c) Glucose level endocrine and circulatory systems

d) pH respiratory, circulatory and excretory systems

The cell is unique because it is only one of its kind ; it is special ; and it belongs to or is

connected with other cells. A cell is unique in terms of it specialisation, division of labour,

coordination and integration. The state of a cell without a particular cellular component can be

predicted based on these principles : specialisation, divison of labour, cooperation and

coordination.

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FOLIO: biology form 4 chapter 2: Cell structure and organisation

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