UNIT1, CELIS

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Learning ObjectivesStructure andfunction of an animal cellStructure and function of a plant cellEssential dffirences between animal and plant cellsCells can dffirentiate into specialised structuresLevel of organisation

CELLS

The detailed structure of a typical animal cell

nucleus

All plants and animals are made of cells. A cell is a unit of life.

It consists of a mass of matter called protoplasm. A protoplasm is made up of cell membrane,cytoplasm and nucleus.

A protoplasm contains 7OIo90% of water, and the rest is made up of mineralsalts and organiccompounds such as carbohydrates, fats and proteins.

The detailed structure of a typical plant cell:smooth ER

nucleus (no ribosomes)

rough ER

ribosome

Golgi apparatusvacuole

cell wall

cell (plasma)membrane chloroplast

mitochondrion cytoplasm

cell (plasma)membrane

cytoplasm

mitochondrion

lysosome

Golgi vesicles

Golgi apparatus

vacuole

rough ERsmooth ER

(no ribosomes)

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Structure of a cell

Plosmo membrone (cell membrone)

Plasma membrane surrounds the entire cell.

It is a thin and delicate which is made up of lipids and proteins.

Plasma membrane is selectively (partially, semi-) permeable. lt controls the passage of food andoxygen into, and waste products out of the cell. ln this way, it maintains a chemical balance withits surrounding medium.

Only plant cells are surrounded by a cell wall made of cellulose. The cell wall is rigid and acts asan important internal support for the plant.

Cytoplosm

Forms the larger part of the cell, made up of 90% water and contains dissolved proteins, sugarsand enzymes.

Numerous chemical reactions occur here.

It also contains larger suspended particles of fats and many structures called organelles.

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Part Function

Mitochondria(singular:

mitochondrion)

a Rod shaped or spherical structures that carry out cellularrespiration to release energy.

Energy is stored in chemical form known as adenosine tri-phosphate (ATP)

Endoplasmicreticulum

The endoplasmic reticulum (ER) are layers of membrane foldedthrough the cytoplasm of a cell forming complex inner surfaces

The ER functions as a pathway for substances to move from onepart of the cell to another

2 types: Smooth ER and rough ER (appears rough due to ribosomesattached to it)

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Vacuoles

Fluid filled cavities

ln a plant cell:,/ One large and central generally

/ Containing cell sap, which is essentially salts and sugarsdissolved in water.

,/ Exerts a fairly high pressure, pushing out on all sides andflattening the protoplasm against the cell wall

,/ Surrounded by a thin membrane called the tonoplast whichfunctions just like the plasma membrane

ln animal cells:./ Small, numerous and temporary

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Nucleus

Spherical body surrounded by a membrane called the nuclearenvelope. The nucleus controls all the activities taking place

in the cell and is also responsible for cell division. Within thenucleus, there are:./ Chromatin: Made up of proteins

and deoxyribonucleic acid (DNA). chromatin

nuclearenvelope

nucleolus

During cell division, they becomevery compact called chromosomes.Chromosomes carry hereditarymaterials cal led genes.

,/ One or more spherical bodiescalled nucleolus (plural: nucleoli),responsible for protein building.

Centriolesa

A small body close to the nucleus that plays a part in cell

division.

Centrioles are generally absent in plants.

Ribosomes

Small spherical structures and sites where proteins are synthesised

in the cell

Found along a network of tubules called the endoplasmic reticulumor floating freely in the cytoplasm

ChloroplastsOnly found in cells of green plants

Contain chlorophyll, which traps light energy for photosynthesis

Golgi apparatusConsists of stacks of flattened membranous sacs and vesicles

involved in processing, packaging and secretion

Differences between plant and animal cells

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ParVStructure Animal cell Plant cell

Cellulose Absent Present

Vacuole Small and numerous vacuoles A large central vacuole

Chloroplasts Absent Present

Centriole Present Absent generally

L. Define organelle.

2. (a) Explain why cells are said to be the building blocks of life

(b) Each living cell contains living material called protoplasm.

(i) Name the three parts that make up the protoplasm of a cell C-;c

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(ii) What is the main constituent in the protoplasm of a cell?

3. The diagram below shows an animal cell.

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(a) Name the labelled structures 1to 13.

1 ...........

3 ...........

(b)

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5

9

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8 7

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11.

13

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What is the collective name for structures 5, 6,7 and 8?

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Label Function

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(c) State the function of the following structures

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2

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4

9

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4. The diagram below shows a plant cell.

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10

9

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(c) What is the function of structure 2?

5. Complete the table to show the differences between an animal cell and a plant cell

CELL DIFFERENTIATION

' Cells have many features in common but their precise structure is closely related to the workthey do.

' Cell differentiation is the process in which a cell becomes specialised for a specific function.For example:

'/ Human cells can be differentiated into liver, muscle, sperm and epithelial cells,/ Plant cells can be differentiated into root hair, xylem, and phloem cells

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Differences Plant cell Animalcel!

Cellwall

Shape

Chloroplasts

Vacuole

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The functions of some specialised tissues are listed below:,/ Root hair cells: absorption of water and mineral salts,/ Xylem vessels: transport of water through conduction and provide support,/ Red blood cells: transport of oxygen

Levels of organisation

. Cells are subunits of organisms and different types of cells may group together to do differentwork.

Part Function

TissueA group of specialised cells working together to carry out a

particular function, eg. muscle tissue, xylem tissue

The body part that is composed of several types of tissues workingtogether to carry out a particular function, eg. heart, brain, flower

Organ systemComposed of several functionally related organs working togetherfor a special function, eg. circulatory system, digestive system

0rganismDepends on their complexity, may comprise of just one cell(amoeba) or millions of cells with a variety of functional units(human being)

OREUISION 2

1. What is differentiation?

2. The table below shows some examples of specialised cells. State how these specialised cellsadapt themselves to perform their functions efficiently.

(a) long and narrowstructu re

Floot hair cell

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(b) lumen

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cell wall

Xylem vessel

(c) biconcaveshape

Red blood cells

3. (a) Define a tissue

(b) Fill in the table below to identify the type of tissues in animals corresponding to theircharacteristics and functions.

Type of tissue Characteristic and function

(i)Cover the internal and external surfaces of the body

Protect the underlying cells from mechanical injury

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(i i)Made up of nerve cells

Send and receive impulses for coordination in the body

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(iii)

Made up of muscle cells that can contract to performwork

Enable body movement by contraction

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(iv)

. Made up of elastic and non-elastic fibres

. Connect the body structures, hold, protect and supportthe cells in the body

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(c) Name two examples of tissues in plants.

4. (a) What is an organ?

(b) Name four examples of organs in the human respiratory system

(c) Name two examples of organs in plants

(b) Give two examples of organ systems in animals.

(c) Give two examples of organ systems in plants.

Section A: Multiple-Choice Questions

The diagram shows cell organisation in an animal. At which stage does cell specialisation takesplace?

ABCDcell -+ tissue -+ organ --> system -+ organism

Which of the following structures are found in both animal and plant cells?

A Cellwall, chloroplasts, vacuole

B Plasma membrane, nucleus, chloroplasts

C Golgi apparatus, mitochondria, plasma membrane

D Vacuole,chloroplasts,mitochondria

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Topical Practice Questions 1

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5. (a) Define organ system.

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