ses biology students companion resources bio score...bio score chapter 2 : cell structure and...

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BIOLOGY STUDENTS COMPANION RESOURCES

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BIO SCORE

CHAPTER 2 : CELL STRUCTURE AND FUNCTIONS

SUBTOPIC : 2.1 Cell as a Unit of Life

LEARNING OUTCOMES: a) Explain the structures of prokaryotic and eukaryotic cells.

b) Describe how cells are grouped into tissues and organs.

MAIN

IDEAS/

KEY POINT

EXPLANATION NOTES

a) Explain the

structures of

prokaryotic

and

eukaryotic

cells.

Prokaryotic

cells

▪ Pro : before, early, primitive, first

▪ Karyon : nucleus

▪ Prokaryotic cell : Cell that has genetic material that is not enclosed by

nuclear membrane.

▪ e.g. of prokaryotic cell: bacteria

Explanation

about structure

of bacteria

(Circular) DNA • Is found in a single and coiled chromosome.

• Not associate with histone protein.

• Not enclosed in a nucleus (lies freely in

cytoplasm).

• Located in a nucleoid region.

Plasmid • Small, double-stranded circular DNA

• Containing extra genes / provide genetic

information for certain activities of cell

Shape • Spherical (cocci)

• Rod-shaped (bacilli)

• Spiral

Glycocalyx /

Capsule • Outside of / external to cell wall

• Made up of polysaccharide and protein

• Protect against immune system of host cell

Cell membrane • Membrane and other structures that surround

and protect the cytoplasm

• Main components are phospholipid bilayer and

embedded proteins

• Control the flow of materials into and out of cell

Cell wall • Made up of peptidoglycan

• Provide structural support and maintain shape of

the bacterial cell

Cytoplasm • Semifluid (water-based) solution

• Composed of water and organic molecules

• Enclosed by plasma membrane

Fimbria (sin.);

Fimbriae (pl.) • Fine, hair-like bristles that present in multiple

numbers

• Help bacterial cell in adhesion to host cell or

other bacterial cell

Pilus (sin.); • Bristle-like structures that present single or in

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MAIN

IDEAS/

KEY POINT

EXPLANATION NOTES

Explanation

about structure

of bacteria

Pili (pl.) pairs

• Longer than fimbria

• Help in adhesion to another bacterial cell during

the transfer of DNA (sex / conjugation pilus)

Flagellum (sin.);

Flagella (pl.) • Long fibers / structures that protrude from the

surface of the bacteria cell

• Mainly for locomotion / movement / motility

Ribosome • Tiny particle compose of RNA and protein

• Site of protein synthesis

Mesosome • Irregular fold in plasma membrane

• Site of cellular respiration

Structure of bacterial cell

Different shapes of bacterial cell

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MAIN

IDEAS/

KEY POINT

EXPLANATION NOTES

Structure of flagella, fimbriae and pilus

Eukaryotic

cells

▪ Eu : true

▪ Karyon : nucleus

▪ Eukaryotic cell : Cell that has genetic material that is enclosed by nuclear

membrane.

▪ E.g. of eukaryotic cell : animal cell, plant cell

Explanation

about

structures of

eukaryotic

cells

▪ Have membrane-bounded nucleus

▪ Nuclear envelope / membrane enclose the nucleus (separating its contents

from the cytoplasm)

▪ Genetic material is linear DNA that is associated with histone protein

▪ Has membrane-bounded organelles

▪ There are two classes of organelles :

1) Endomembrane system : organelles that communicate with one another

via small vesicles or membrane channels

2) Energy related organelles such as mitochondria, chloroplasts

DNA associate with histone protein

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MAIN

IDEAS/

KEY POINT

EXPLANATION NOTES

Structure of an animal cell

Structure of a plant cell

b) Describe

how cells are

grouped into

tissues and

organs.

1. Cells are the simplest unit of life.

2. Individual cells are specialized to perform specific functions that help to

maintain homeostasis and benefit the body as a whole.

3. Groups of cells that are similar in structure and perform a common or related

function are called tissues.

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MAIN

IDEAS/

KEY POINT

EXPLANATION NOTES

4. There are four basic types of tissue in the human body:

• Epithelial tissues

• Muscle tissues

• Nerve tissues

• Connective tissues

5. Two or more tissues that come together to form a spesific function for the

body.

• Eg : Stomach

✓ Lining by epithelium tissues : produces digestive juices.

✓ Wall made up by muscle tissues : churns and mixes stomach contents.

✓ Connective tissues : reinforces the soft muscular walls.

✓ Nerve fibers : increase digestive activities by stimulating the muscle to

contract more vigorously.

✓

Cell Differentiation

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MAIN

IDEAS/

KEY POINT

EXPLANATION NOTES

Level of Cellular Organization

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BIO SCORE

CHAPTER 2 : CELL STRUCTURES AND FUNCTIONS

SUBTOPIC : 2.2 Structures and functions: plasma membrane and organelles

LEARNING OUTCOMES:

a) Show the detailed structures of typical plant and animal cells and state the organelles present.

b) Explain the structures and functions of the following organelles : nucleus, rough endoplasmic

reticulum, smooth endoplasmic reticulum, Golgi body, lysosome, ribosome, mitochondria,

chloroplast and centriole.

c) Show the structure of plasma membrane based on Fluid Mosaic Model.

d) Explain the structure of the plasma membrane and the functions of each of its components.

MAIN IDEAS/

KEY POINT EXPLANATION NOTES

a) Show the detailed

structures of

typical plant and

animal cells and

state the

organelles

present.

Detailed structures

of typical plant and

animal cells

Animal cells seen under light compound microscope

Plant cells seen under light compound microscope

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Detailed structures

of typical plant and

animal cells

Animal cells seen under electron microscope

Plant cells seen under electron microscope

Organelles present in

plant and animal

cells

Organelles in animal cell

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Organelles present in

plant and animal

cells

Organelles in plant cell

b) Explain the

structures and

functions of the

following

organelles :

nucleus, rough

endoplasmic

reticulum,

smooth

endoplasmic

reticulum, Golgi

body, lysosome,

ribosome,

mitochondria,

chloroplast and

centriole.

Organelle :

▪ Structures that suspended within cytosol and perform specific

functions inside cell.

▪ Can be divided into membranous organelles and non-

membranous organelles

Membranous

organelles

Non-membranous

organelles

Nucleus

Chloroplast

Mitochondria

Rough ER

Smooth ER

Golgi apparatus

Lysosome

Ribosome

Centriole

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Explanation on the

structures and

functions of

organelles

Organelles Structures Functions

Nucleus ▪ Spherical or oval in shape

▪ Double membrane nuclear

envelope enclose the

nucleus and separate it

from cytoplasm.

▪ Has outer membrane that

is continuous with

endoplasmic reticulum

and also has inner

membrane

▪ Inner part of nucleus is

nucleoplasm which is

semifluid medium

containing chromatin,

nucleotides, mineral ions,

enzymes and nucleolus

▪ Surface of nuclear

membrane has nuclear

pore that regulate the entry

and exit of molecules e.g.

protein, RNA from

nucleus.

▪ Nucleolus is small dense

spherical body within

nucleus that consist of

RNA and protein

• Store genetic

information /

genes of a cell :

contain

chromatins /

chromosomes

in nucleoplasm

• Control

production of

RNA and

proteins in cell

• Control all

activities of cell

by regulating

synthesis of

proteins and

enzymes

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Explanation on the

structures and

functions of

organelles

Rough

endoplasmic

reticulum (ER)

▪ Consist of

network of

membranous

flattened sacs

called cisternae

▪ Membrane of ER

separate the ER

lumen @ cavity /

cisternal space

from the cytosol

▪ Membrane of

rough ER is

continuous with

the outer

membrane of

nucleus

▪ There are

ribosomes on

outer surface of

the rough ER

membrane

⚫ Synthesis secretory

proteins (e.g.

hormone)

- polypeptides

synthesized by

ribosomes are

transported to

ER lumen

- inside ER

lumen, the

polypeptides

are modified by

enzymes (add

carbohydrate

chain to the

protein

forming

glycoprotein)

⚫ Involve in

intracellular

transport of

proteins (the

glycoprotein is

packaged inside

transport vesicle and

the vesicle is carried

to Golgi body)

Smooth ER ▪ Consist of

network of

membranous

tubules called

cisternae

▪ Membrane of ER

separate the ER

lumen @ cavity /

cisternal space

from the cytosol

▪ Lack of

ribosomes on

outer surface of

the smooth ER

membrane

⚫ Site of lipid

synthesis

⚫ Breakdown of

stored glycogen to

glucose in liver

⚫ Store calcium ions

in sarcoplasmic

reticulum of skeletal

muscle

⚫ Detoxify drugs and

poison in liver

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Explanation on the

structures and

functions of

organelles

Golgi

apparatus /

body

▪ Consist of a group of

flattened membranous

sacs called cisternae

▪ Each cisterna has lumen

▪ Has two sides : cis face

and trans face

▪ Cis face is usually

located near the ER and

receive transport

vesicles from ER

▪ Trans face bud off

transport vesicles

containing specific

products to be carried to

other locations inside

cell or to plasma

membrane for secretion

▪ Modify,

packaging and

sorting of

protein

• Cis face

receive

transport

vesicles

from ER

• Products of

ER are

modified

during

their transit

from cis face

to trans face

of Golgi body

• Trans face

package the

modified

products in

transport

vesicles and

sort the

vesicles

to be

transported

out of Golgi

body

▪ Form

lysosome

▪ Form

polysaccharide

s e.g. pectin in

Golgi body of

plant cells

which then

incorporated

with cellulose

into cell walls

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MAIN IDEAS/

KEY POINT

EXPLANATION NOTES

Explanation on the

structures and

functions of

organelles

Lysosome ▪ Spherical in shape

▪ Single-membrane

bounded organelle

▪ Produced by Golgi

apparatus

▪ Contains hydrolytic

enzymes

3) Involve in

intracellular food

digestion

(phagocytosis)

4) Involve in

autophagy

(digestion of old

@ worn out

organelles)

5) Involve in

autolysis

(digestion of old

@ damaged cells

results in

apoptosis

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Ribosome ▪ Not bounded by

membrane

▪ Are complexes made

of ribosomal RNA

(rRNA) and protein

▪ Consist of two

subunits : large

subunit and small

subunit

▪ Can be found as free

ribosomes

(suspended in

cytosol) and bound

ribosomes (attach to

rough ER)

⚫ Site of protein

synthesis

- most of the

proteins made

by free

ribosomes

function within

cytosol

- bound

ribosomes

make proteins

that

are inserted into

membranes, for

packaging

within

organelle e.g.

lysosome or

secretory

proteins

Mitochondria ▪ Rod-shaped

▪ Double membrane-

bounded organelle :

- smooth outer

membrane

- highly folded inner

membrane forming

cristae

▪ Cristae is highly folded

to increase the surface

area of inner membrane

thus increasing the

efficiency of energy /

ATP production

▪ Intermembrane space is

⚫ Site of cellular

respiration /

energy @ ATP

production

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the narrow region

between outer and inner

membranes

▪ Mitochondrial matrix

containing enzymes,

DNA and ribosomes is

enclosed by the inner

membrane

Chloroplast ▪ Double membrane-bounded

organelle

▪ Outer and inner membrane is

separated by very narrow

intermembrane space

▪ Inside chloroplast is another

membranous system in the

form of flattened,

interconnected sacs called

thylakoids

▪ Stack of thylakoids are called

granum

▪ Thylakoid membrane contain

photosynthetic pigments e.g.

chlorophyll

▪ Fluid outside thylakoid is

stroma which contain

enzymes, DNA and ribosomes

▪ Site of photo-

synthesis

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MAIN IDEAS/


Explanation on the

structures and

functions of

organelles

s

Endomembrane System:

• Components of endomembrane system includes the nuclear

envelope, endoplasmic reticulum, Golgi apparatus, lysosome,

various kinds of vesicles, vacuoles and plasma membrane.

• The system carries out variety of tasks in the cell, including

synthesis of proteins, transport of proteins into membranes

and organelles or out of the cell, metabolism and movement

of lipids and detoxification of poisons.

• The membranes of this system are related either through direct

physical continuity or by formation of vesicles (membranous

sacs).

Centriole ▪ In animal cells,

microtubules grow out

from centrosome (region

that is located near the

nucleus)

▪ Within the centrosome of

animal cells, is a pair of

centrioles

▪ Each centriole is

composed of nine sets of

triplet microtubules

arrange in a ring

⚫ May help

to organize

the spindle

fibre

during

mitosis and

meiosis in

animal

cells

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c) Show the

structure of

plasma

membrane based

on Fluid Mosaic

Model.

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d) Explain the

structure of plasma

membrane and

functions of each of

its components

▪ Fluid Mosaic model is proposed by Singer and Nicolson

▪ Fluid because phospholipids and proteins are able to move

laterally / side by side in the phospholipids bilayer

▪ Mosaic because arrangement of different proteins partially or

fully embedded or attached to the phospholipids bilayer

▪ Two main components of plasma membrane are phospholipids

and proteins

▪ Phospholipids are amphipathic molecules that means have

both hydrophobic and hydrophilic regions

- hydrophilic head

- hydrophobic tail

▪ Importance of hydrophobic regions in plasma membrane :

- allow the cell membrane to be selectively permeable

- allow movement of lipid soluble molecules

- reduce loss of water from inside cell

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MAIN IDEAS/


Explanation on the

structure of plasma

membrane and


its components

▪ Cholesterol are found in plasma membrane of animal cells

between the tails of phospholipids

▪ Function of cholesterol is to regulate fluidity of membrane

under the influence of temperature

- reducing fluidity of membrane / membrane less fluid at warm

/higher temperature

- membrane more fluid at lower temperature

▪ Two types of membrane proteins :

- intrinsic @ integral protein (either fully or partially embedded

in phospholipids bilayer)

- peripheral @ extrinsic protein (attach to phospholipids

bilayer)

▪ Functions of membrane proteins :

- as transport protein

- as enzymes

Channel

protein

Carrier protein

(for passive

transport)

Carrier protein

(for active

transport)

Has specific active site that binds with specific substrate during enzymatic reactions

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MAIN IDEAS/


Explanation on the

structure of plasma

membrane and

functions of each of its

components

- involve in signal transduction / as cell surface receptor

- as intercellular joining / involve in cell adhesion

- as cell surface identity marker or involve in cell

recognition

- provide attachment site for cytoskeleton and

extracellular matrix

Act as receptor that has

specific binding site for

signaling molecule e.g.

hormone

Membrane proteins of neighboring cells are joined together forming tissue e.g. epithelial cells

Helps to maintain cell

shape and

to stabilize location of

certain membrane

proteins

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MAIN IDEAS/


Explanation on the

structure of plasma

membrane and


its components

▪ Carbohydrate chains attach to protein forming glycoprotein

(e.g. variation in carbohydrate chain of glycoproteins on the

surface of RBC contribute to the 4 human blood types A, B,

AB and O)

▪ Carbohydrate chains attach to lipid forming glycolipid

▪ Importance of membrane carbohydrates in cell-cell

recognition :

- sorting of cells into tissues and organs in animal embryo

- basis for rejection of foreign @ non-self tissue by immune

system (e.g. MHC marker)

- enable cell recognize other cell by binding to molecules

containing carbohydrates on extracellular surface of plasma

membrane

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BIOLOGY SCORE

CHAPTER 2: CELL STRUCTURE AND FUNCTIONS SUBTOPIC : 2.3 Cells are grouped into tissues (animal tissues)

LEARNING OUTCOMES : (a) Describe animal tissues.

(b) State the types, structures, functions and distributions of the following

tissues:

(i) Animal cells & tissues:

Epithelial cells (simple squamous, simple cuboidal, simple columnar),

nerve cell (motor neuron),muscle cells(smooth muscle),connective

tissues(blood)

MAIN IDEAS/


a) Describe

animal tissues.

▪ A group of similar cells and their intercellular substance joined together to

perform a specific function.

Types of animal

tissues

Four basic types according to their function and structure:

▪ Epithelial tissues

▪ Nervous tissues

▪ Muscle tissues

▪ Connective tissues

b) State the

types,

structures,

functions and

distributions of

animal cells

and tissues

A. Epithelial

cells

Structure:

- Consists of cells arranged in continuous sheets, in single or multiple layer.

- Closely packed and held tightly together by many cell junction.

- Has little intercellular space.

- Avascular (without blood vessels).

- Has a free surface.

- Has microvilli (intestine) and cilia (trachea).

Functions

- Secretion

- Absorption

- Protect external and internal body surfaces from microbes, chemical,

dehydration and friction.

Distribution

- Rest on basement membrane.

- Covers a body surface (epidermis).

- Line inner body cavity, tubes and blood vessels.

- Cover the thoracic and abdominal organ.

- Also found in gland.

Classification:

• Based on shape and number of cell layers.

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MAIN IDEAS/


Types of

Epithelium

Tissue

Types of Epithelial Tissue:

▪ Simple Squamous

▪ Simple Cuboidal

▪ Simple Columnar

▪ Stratified Squamous

Types Structure Distribution Function

Simple

squamous

• A single

layer of

flattened

cells with

disc-shaped.

• Central

nuclei.

• Air sacs of

lungs

• Glomerular

capsule of

Kidney

• Lines of heart

• Blood vessels

• Allow passage of materials

by diffusion and filtration

where protection is not

important.

Simple

cuboidal

• Single layer

of cube-

shaped

cells.

• Large &

spherical

central

nuclei.

• Thicker

than simple

squamous.

• Kidney tubule

• Ovary surface

& testes

• Ducts and

secretory

portions of

small gland

• Secretion of hormone or

saliva. (Salivary & Thyroid

gland.)

• Absorption (Reabsorption

of molecules by Proximal

Convoluted tubule in

kidney.)

Simple

columnar

• Single layer

of

rectangular/

tall cells.

• Nuclei

(round or

oval) near

base of

cells.

• Goblet cells

& cells with

microvilli &

cilia.

•

• Gallbladder

• Duct of gland

• Lines the

gastrointestinal

tract

• Uterine tube

• Bronchi.

• Secretion of enzymes,

mucus and other

substances.

• Ciliated type propels

mucus or reproductive cells

by ciliary action

• Absorbing nutrients.

B. Nervous

tissues

Structure

▪ Made up of neuron and neuroglia (supporting cells).

▪ Neurons consist of:

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- dendrite

- cell body

- axon

▪ Axon

- Single extension of cytoplasm.

- Function: conducts impulse away from the cell body.

-

▪ Dendrite

- Highly branched extensions.

- Function: conduct signals toward the cell body.

-

▪ Node of Ranvier

- Small uncovered parts of axon between the myelin

sheath.

- Function: Site for accelerating impulse transmission.

▪ Myelin sheath

- Layer of fatty material (surround the axons).

- Produce by Schwann cell.

- Function: Protects axons and provide

electrical insulation.

▪ Neuroglia

- Supports and nourish the neurons.

- Example: Schwann cell

Function: to transmit impulse.

Distribution: Brain, spinal cord and nerves.

C. Muscle

tissues

Structures

- Muscles are responsible for all types of body movement

- Composed of muscle fibers (cell)

▪ Smooth Muscle

- Lack striation

- Spindle-shaped cells

- Single nucleus

- Involuntary control

Functions: Propel substances of objects (foodstuff) along internal passageways

Distribution: Wall of internal organs (digestive tract) or hollow organs

Structure of smooth muscles

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D. Connective

tissues

Structure

▪ Animal tissue that functions mainly to bind and support other tissues, having

a sparse population of cells scattered through an extracellular matrix.

General functions:

- Provide support, strength and flexibility.

- Transport of material.

- Store energy.

- Defend body against pathogens.

Types of connective tissues

▪ 1. Blood

Consist of:

• Extracellular Matrix:

- Plasma (water, salts and dissolved proteins)

• Cells

- Erythrocytes

- Leukocytes

- Platelets

A. Erythrocytes: red blood cells

- Biconcave disc-shape

- Lack of nuclei

- Thinner in the center than at its edge

- Contain haemoglobin, enzyme and

inorganic ions

- Function:

Transport oxygen, carbon

dioxide, nutrients and waste

B. Leukocytes: white blood cells

- Larger than erythrocytes

- Spherical in shape

- Have nucleus and organelles

- Two types:

- Granulocytes: Granular cytoplasm and

lobed nuclei

- Agranulocytes: Clear cytoplasm and

nuclei not lobed

- Functions:

• Responsible for antibody production and other specific defense

against pathogens

• Lymphocyte B: Produce antibody

• Neutrophils and Monocytes: Engulf foreign substances

C. Platelets

- Fragments of cells broken off from large cells in the bone marrow

- No nuclei

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- Functions:

• Blood clotting

• Repair gaps in the wall of blood vessel

Blood cells organization

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BIO SCORE

CHAPTER 2: CELL STRUCTURE AND FUNCTIONS SUBTOPIC : 2.3 Cells are grouped into tissues (plant tissues)

LEARNING OUTCOMES : (a) Describe plants tissues.

(b) State the types, structures, functions and distributions of the following

tissues:

ii. Plant cells & tissues:

Apical meristem, ground (parenchyma, collenchyma,

sclerenchyma),vascular (xylem and phloem)

MAIN IDEAS/


(a) Describe

plants tissues

▪ There two main types of plant tissues.

1. Meristematic tissue

Apical meristem

2. Permanent tissue

a. Ground tissue

b. Vascular tissue

(b) The types,

structures,

functions and

distributions

of plant cells

and tissues:

1. Meristem

tissues

▪ Meristem Tissue: Undifferentiated embryonic tissue in the active growth

regions of plants

Apical meristem

▪ Structure:

- Cells are small and isodiametric

- Have large nucleus

- Have dense cytoplasm and few organelles

- Closely packed

- Have thin primary cell wall

- Cell actively divided

▪ Functions:

1. Elongate shoots and roots.

2. Produce primary plant body.

▪ Location: Shoot tips and root tips

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MAIN IDEAS/


2. Permanent

Tissues

a) Ground

tissues

Structure Parenchyma Collenchyma Sclerenchyma

Shape Isodiametric Polygonal Various shape

and size

Cell wall

• Thin and flexible

primary wall

• Contain cellulose,

hemicellulose and

pectin

• Permeable to water

and permit passage

of solutes

• No secondary wall

• Primary wall is

thicker than

parenchyma

• Contain cellulose,

hemicellulose and

pectin

• Uneven

thickening occur

at the corners of

the walls

• No secondary

wall

• Pits are present in

the wall

• Tough and thick

secondary cell

walls

impregnated

with lignin

• Pits are present

in the walls

Cell

arrange

ment

• Cell are loosely

packed together

• Many large

intercellular air

space

• Cells are closely

packed together

• No intercellular

air spaces

• Cells are

closely packed

together

• No

intercellular

air spaces

Living/

dead at

maturity

Living at maturity Living at maturity

• Dead at

maturity

• Lack living

protoplasts

when they

mature

• Two types:

• Fiber

• Long and

slender

• Group

together

in strands

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MAIN IDEAS/


• Tapering

Ends

• Sclereids

• Shorter

than fiber

• Irregular

in shape

• Thick

wall

• Lignified

secondar

y wall

Parenchyma Collenchyma Sclerenchyma

Distribution - Cortex of stem

- Cortex of roots

- Mesophyll

- Pulp of fruit

- Endosperm of

seed

- Outer regions of

cortex

- Below the

epidermis of

leaves, petioles

and soft stems of

dicot plant

- Leaf veins

- Young stem

Fiber:

- Below the

epidermis of

stem or roots

- Around

vascular

bundle

Sclereid:

- Stem, leaves

and seeds

- Fruits (pears

and guava)

Function - Photosynthesis.

- Gaseous

Exchange and

buoyancy for

aquatic plants

(Intercellular air

spaces).

- Packing tissues

(around vascular

tissues).

- Food storage

- Secretion (Sugary

nectar, hormones,

enzymes and

tannins).

- Supporting tissue:

provide the

herbaceous plant

with mechanical

strength and

flexibility.

- Provide much of

support for stem

in which

secondary

growth has not

taken place.

- Photosynthesis:

some

collenchyma

contain

chloroplast

Fiber:

- Acts as

supporting

tissue.

Sclereid:

- Protective

tissue: gives

strength and

support to the

plant structure

or organ.

2. Vascular

Tissue

▪ Involves in transport of materials around the plant body.

▪ Two types:

- Xylem: Vessel Elements and Tracheid

- Phloem: Sieve tube and Companion cell

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MAIN IDEAS/


Types Structure Function

Xylem

Vessel

element

- Secondary wall: lignin

- Ends open and connect to one

another to form long pipes

- Dead cells with hollow lumen

- More water can flow with less

friction

Transport

water and

dissolved

minerals from

the roots to the

leaves

Tracheid

- Thick lignified

- Lumen: small and hollow when

mature

- Tapering end wall

- Lots of pits: allow water to move

to another tracheid also

surrounding living cells

Types Structure Function

Phloem

Sieve tube

- Consist of sieve elements (sieve

cells) joined together to form a

long tube.

- End walls are perforated forming

sieve plates with sieve pores.

- Cells are alive, with thin cellulose

walls and protoplasm.

Transport

organic

material

(photosynthesi

s) from one

part of the

plant to

another.

Companion

cell

- Located beside the sieve tube.

- Have a nucleus, dense cytoplasm

with small vacuoles.

- Metabolically active (have

mitochondria and ribosomes).

- Linked to sieve elements by

numerous plasmodesmata.

Provide ATP

for active

transport

during

transportation

of organic

material.

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MAIN IDEAS/


Xylem

Vessel element Tracheid

Phloem

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BIO SCORE

CHAPTER 2: CELL STRUCTURE AND FUNCTION SUBTOPIC : 2.4 Cell Transport

LEARNING OUTCOMES : a) Describe the following processes:

i. Passive transport (simple diffusion, facilitated diffusion,

osmosis)

ii. Active transport (sodium-potassium pump)

MAIN IDEAS/


Transport

Across

Membrane

▪ Process to move substances across the cell membrane (plasma membrane)

are essential to the life of the cell.

- Example: Gaseous exchange

▪ Plasma membrane regulates the passage of molecules into and out of the

cell.

- Enable a cell to control substances and how much of each enters or

leaves the cell

- It allows the cell to maintain a difference between its internal

environment and extracellular fluid.

- It supplies the cell with nutrients, removes wastes and maintains

volume and pH.

▪ Plasma membrane is selectively permeable.

- Only allow some material to pass.

- Inhibits passage of other materials.

(i) Passive

transport

▪ Diffusion of solute across membrane.

▪ From high concentration region to low concentration region.

▪ Does not require energy/ ATP.

▪ Down concentration gradient.

▪ Until equilibrium is achieved.

▪ 3 types:

- diffusion

- facilitated diffusion

- osmosis

1. Simple

diffusion

▪ Diffusion of solute directly through phospholipid bilayer to move across a

plasma membrane.

▪ Example of solutes/molecules are lipid soluble molecule, oxygen gas,

carbon dioxide.

2. Facilitated

diffusion

▪ Carrier-assisted diffusion of molecules across a cell membrane through

specific channels from a region of higher concentration to lower

concentration.

▪ Help/aid by carrier protein and channel proteins

▪ The process is driven by concentration gradient

▪ Does not require energy/ ATP

▪ Example of molecules are glucose, fructose, amino acids, some vitamins,

urea

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MAIN IDEAS/


▪ Carrier protein:

- bind to molecule and change their shape to move specific molecules in

or out of the cell

- example: glucose

▪ Channel protein:

- have a tunnel that allow movement of ions or charge molecules to move

in or out of the cell

- example: sodium ion or chloride ion

Comparison

between

simple diffusion

and

facilitated

diffusion

Simple diffusion Facilitated diffusion

Through the phospholipid bilayer Through the transport protein (carrier

or channel protein)

Happens to the small and non-polar

particles

Happens to large and polar particles

Movement of molecules occur down the concentration gradient

Not require energy

3. Osmosis ▪ The movement / diffusion of water across a selectively permeable

membrane from area of higher water potential to area of lower water

potential.

▪ Water potential: ψ (psi)

▪ Water molecules move from hypotonic solution to hypertonic solution until

solution are isotonic.

Concept of

water potential

▪ Water potential is free energy / potential energy of water.

▪ The tendency of water molecules to enter or leave from the solution by

osmosis.

▪ Unit of water potential is kilopascal (kPa)

▪ Components of water potential:

- solute potential

- pressure potential

▪ Formula of water potential:

Ψ = Ψp + Ψs

Water potential = pressure potential + solute potential

▪ Solute potential:

- A measure of the change in water potential of the system due to the

presence of solute molecules.

- usually negative value.

▪ Pressure potential:

- The component of water potential due to the hydrostatic pressure that is

exerted on water in a cell.

- usually positive value.

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MAIN IDEAS/


▪ What happen to animal cell and plant cell in different tonicity of solution?

ii. Active

transport

▪ The movement of molecules / ions from a region of lower concentration

region to a region of higher concentration region// against concentration

gradient

▪ Require energy in the form of ATP

▪ Require transport / carrier / pump protein

▪ Example is Sodium-potassium pump

Sodium-

potassium pump

▪ Concentration of sodium ions (Na+) is higher outside of the cell; meanwhile

concentration of potassium (K+) ions is higher inside of the cell.

▪ For each cycle, Sodium- potassium pump transport THREE intracellular

Na+ out of the cell and TWO extracellular K+ into the cell.

▪ Involve phosphorylation; the addition of phosphate group; which cause the

changes in conformation of protein.

Mechanisms /

steps in sodium

potassium pump

▪ 3 intracellular Na+ bind to specific site on carrier / pump protein

▪ The binding stimulates phosphorylation of carrier protein by ATP

▪ The phosphorylation causes the protein to change its conformation

▪ Causing expel of Na+ to the outside of cell.

▪ 2 extracellular K+ bind to specific site on carrier protein

▪ The binding triggers release of phosphate group from carrier protein

▪ Loss of phosphate restore original conformation of carrier protein

▪ K+ is released into the cell

▪ The cycle is repeated.

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MAIN IDEAS/


Sodium-Potassium Pump

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