Topic 1- Introduction to Cell

8/12/2019 Topic 1- Introduction to Cell

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Topic 1

Introduction to cell


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Biologyis the systematic study of life

The branch of science that is concerned with

the study on life and living organisms

The characteristics of life: All living organismsshare the following characteristics of life:

i) Organization: the levels of biological organization

extend as follows:

Introduction


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ii) Acquisition of materials and energy from the

environment

iii) Reproduction: they produce offspring

iv) Respond to stimuli: they react to internal and

external events

v) Internal homeostasis

vi) Growth and developmentvii) Adaptations to a changing environment


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The Diversity and Unity of Cells

Cells are the fundamental units of all living

things

Although the diversity organisms isincredible, the cells of all organism share

many similarities.

Only a few structural differences betweenmost types of cells.


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Cell Theory

All organisms are composed of one or

more cells.

Cells are the basic living unit of structureand function in organisms.

All cells come only from other cells.


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Cell Theory (cont.)

Four generalizations constitute the cell theory:

1. Every living organism consists of one ormore cells

2. A cell is the smallest unit of life, individuallyaliveeven as part of a multicelled organism

3. All living cells come from division ofpreexisting cells

4. Cells containhereditary material, which

they pass to their offspring during division


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Two main types of cells

There are 2 components to the cell theory.

i) All organisms are composed of cells.

ii)Cells come only from preexisting cells.

All cells have an outer membrane called theplasma membrane.

The plasma membrane encloses asemifluid substance called thecytoplasmand the cells genetic material.


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The word cellentered biology in the 17thcentury.

Anton van Leeuwenhoekis recognized forinventing one of the earliest microscopes and

observing a first cell.

Robert Hookeconfirmed earlier findings andcoined the term cell.

Matthias Schleidenstated that plants are

composed of cells.

Theodore Schwannstated that animals are

composed of cells.


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Size of Cell

Cell size varies, but are quite small.

A frogs egg is about 1 millimeter (1mm) in

diameter. Large enough to be seen by naked eye

Most cells are smaller than 1mm.

Some cells are as small as 1 micrometer

(1mm).


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Size of Cell (cont.)

Cells being small is an advantage formulticellular organisms:

Nutrientssuch as glucose can enter thecell.

Wastessuch as CO2 can exit cell.

Therefore surface area affects the ability toget materials in and out of a cell.

As cells increase in volume, the proportionateamount of surface area decreases.


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Size of Cell (cont.)

For a cube-shaped cell:

The volumeincreases by the cube of the

sides (height X width X depth). The surface area increases the square of

the sides and the number of sides (height

X width X 6). If a cell doubles in size, its surface area

increases fourfold, while the volume

increases eightfold.


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Surface Area / Volume Ratio

All 3 have the same volume, but the group

on the right has 4 times the surface area

One 4-cm cube Eight 2-cm cubes Sixty-four 1-cm cubes

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.


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How scientist study cells?

Most cells are far too small to see withthe naked eye

We use different types of microscopes

and techniques to reveal cells andtheir internal and external details

Cells under the microscope


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Cells under the microscope (cont.)

Our bodies are comprised of severalhundred different types of cells, withbillions of each cell type present.

Each type of cell is specialized in itsparticular function.

Cells are so small that a microscope isneeded to see them.


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Types of microscopes

1. Light microscopes

2. Phase-contrast

microscopes

3. Fluorescence

microscope

4. Electronmicroscopes

5. TransmissionelectronMicroscopes

6. Scanning electronmicroscopes


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Examples of microscopes

Compound light microscope Transmission electronmicroscope (TEM)


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phosphor

screen

incoming electron beam

condenser

lens

specimen

on gridobjective

lensprojectivelens

Transmission electron microscope (TEM)


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Light microscopes can be used to view

cells but not in much detail.

Electron microscopes allow the

structure of cells to be viewed in greater

detail.


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Sizes of Living Things

10 m1 m0.1 m1 cm1 mm100 m10 m100 nm10 nm1 nm0.1 nm

mousefrog egg

human eggmost bacteria

virus

protein

atomant

electron microscope

light microscope

human eye

human

blue whale

chloroplastrose

1 km100 m1 m

amino

acids

plant and

animal

cells

ostrich

egg

Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.


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ALight micrograph. BLight micrograph. CFluorescence

micrograph.

DA transmission

electron micrograph

reveals fantastically

detailed images of

internal structures.

E A scanning

electron micro-graph

shows surface

details. SEMs may beartificially colored to

highlight specific

details.

A reflected light

microscope captures

light reflected fromspecimens.

A phase-contrast

microscope yields high-

contrast images oftrans- parent

specimens. Dark areas

have taken up dye.

This image shows

fluorescent lightemitted by

chlorophyll

molecules in the

cells.

Different views of different microscopes, reveal

different characteristics of the same organism


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Cells are small because they are limited bytheir surface-area-to-volume-ratio.

The surface area of a cell is critical because

it must be large enough to allow adequatenutrients to enter the cell.

Cells can increase their surface area with

specialized projections such as microvilli.


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Traits common to all cells

Cells differ in size, shape, and function.

Although cells differ in size, shape andfunction, each starts out with a plasmamembrane, cytoplasm, and a region of

DNA (in eukaryotic cells, a nucleus)

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Topic 1- Introduction to Cell