Transcript Cells: `Structure & Function`

Cells:
‘Structure & Function’
Chapter 2
Pages 22-50
Chapter 2 - Cells: Structure &
Function
1
Looking at Cells

Examination of cells using microscopes
reveals much about their internal organisation.

Each living cell is a small compartment with an
outer boundary known as the cell membrane
or plasma membrane.

Inside each cell is a fluid known as cytosol,
that contains fluid and many vital substances
for the cell.
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Function
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Looking at Cells

Living cells can be divided into 2 distinct
groups according to the organisation of their
internal structures.

Prokaryotic Cells – Lack of a nucleus or clear
structure to house their DNA. (ie bacteria)

Eukaryotic Cells - Contain structures called
organelles and the DNA is enclosed inside a
membrane bound nucleus. (ie plants, animals,
fungi & protists)
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Function
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The Cell Membrane

The boundary of all living cells is the cell membrane. It
controls entry of dissolved substances into and out of
the cell.

The cell membrane is ultra thin (thickness <0.01
micrometers).

A cell membrane contains both lipids and protein.

It consists of a double layer of lipids, in which proteins
are embedded, forming a channel to allow certain
substances into and out of the cell.
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Function
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The Cell Membrane
Fig 2.4 – Fluid
Mosaic Model
p25
Activity Sheet – Structure of Membranes
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Function
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Movement In
and Out of Cells

In order to survive, cells need to
take in and expel substances.

Cells generally let in particular dissolved
substance. It is therefore said to be partially
permeable. Fig 2.5 p25

Dissolved substances that pass across the cell
membrane, does so by two processes –
Diffusion & Active Transport.
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Function
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Free Passage - Diffusion

Diffusion is the net movement of a substance
(solution), from a region of high concentration to a
region of low concentration.

Diffusion does not require energy.

Fig 2.7 – Diffusion in action p27
Chapter 2 - Cells: Structure &
Function
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Free Passage - Diffusion

One special case of diffusion is known as
osmosis. The process of osmosis is the net
movement of water particles by diffusion in or
out of a cell.

Osmosis – A Special Diffusion Case p28
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Free Passage - Diffusion

Substances that dissolve in water are hydrophilic ‘water
loving’.

Substances that don’t dissolve are called lipophilic or
hydrophobic.
Alcohol is a lipophilic substance.


Lipophilic substances enter the cell by absorbing through
the lipid layer of the membrane.

This is known as lipid diffusion. The body absorbs
alcohol using this method.
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Function
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Free Passage - Diffusion

Solid particles (ie molecules) and those that cannot enter
via the lipid layer, enter the cell through a specific carrier
protein in the membrane. This is known as facilitated
diffusion.

Fig 2.9a – Facilitated diffusion

Facilitated diffusion travels from an area of high
concentration to an area of low concentration.
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Function
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Active Transport

Active transport is the net movement of dissolved
substances into or out of the cell against a
concentration gradient (opposite to facilitated
diffusion).

Active transport requires energy to perform.

Active transport enables cells to maintain stable
internal conditions in spite of extreme external
surroundings.
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Function
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Diffusion & Active Transport

Fig 2.9b – Active Transport

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Function
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Bulk Transport

When bulk material is
taken into a cell as a
solid, the process is
termed
‘Phagocytosis’.

When bulk fluid is
taken into a cell as
fluid, the process is
termed ‘Pinocytosis’.
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Function
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Bulk Transport - Endocytosis

Unicellular protists (Amoeba) obtain their
energy in the form of relatively large food
particles that they engulf.

The food gathers at the lipid layer of the
membrane and is drawn in and enclosed within
a sac where the food is digested.

This process of bulk material into a cell is
known as endocytosis.
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Bulk Transport - Endocytosis

Fig 2.11a – Example of Endocytosis
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Bulk Transport - Endocytosis

Fig 2.11b – Example of Endocytosis
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Bulk Transport - Exocytosis

Bulk transport out of cells (export or
waste material) is called exocytosis.

In exocytosis, vesicles formed within a
cell fuse with the plasma membrane
before the contents of the vesicles are
released from the cell.
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Bulk Transport - Exocytosis

Fig 2.13 – Exocytosis

Activity Sheet – Exocytosis & Endocytosis p101
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Cell Walls

The cell membrane forms the exterior of
animal cells.

However, in plants, fungi and bacteria, a rigid
cell wall lies outside the cell membrane.

The cell wall varies in composition between
plants, fungi and bacteria.
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Cell Walls

Quick Check Questions 1-3 p31
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Function
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Cell Organelles
“The nucleus – control centre”

The control centre of the cells of animals,
plants, algae and fungi is the nucleus.

The nucleus forms a distinct spherical structure
that is enclosed within a double membrane
known as the nuclear envelope.

Cells that have a membrane bound nucleus
are called eukaryote cells.
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Cell Organelles
“The nucleus – control centre”

Cells that lack a nuclear envelope or nucleus are called
prokaryote cells.

Cells of organisms such as bacteria, contain genetic
material (DNA) that is not enclosed within a distinct
nucleus.

The nucleus contains many granules that are made of the
genetic material Deoxyribonulceic Acid (DNA).

During cell reproduction, the DNA granules arrange
themselves into rod-shaped granules called
chromosomes.
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Cell Organelles
“The nucleus – control centre”

The nucleus also contains one or more
large inclusions known an nucleoli
which are composed of ribonucleic acid
(RNA).
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Organelles
Mitochondrion “Energy Factories”

Living cells require energy all the time.

The useable energy supply for cells is ATP (adenosine
triphosphate).

ATP is produced in cells during a process called cellular
respiration.

In eukaryote cells, energy is synthesised in
mitochondrion, which are found in the cytoplasm.

Prokaryote cells do not have mitochondrion.
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Organelles
Mitochondrion “Energy Factories”
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Function
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Organelles
Ribosomes “Protein Factories”

Cells must produce proteins in order to perform
specialised functions.

Haemoglobin-oxygen transport
Insulin-blood sugar conversion


Ribosomes are the organelles where protein
production occurs.

Ribosomes are part of the cytoplasm and can only
be seen through a TEM.
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Organelles
“Endoplasmic Reticulum”

Protein molecules produced by ribosomes
need a transport system to exit the cell and
reach its target cell/destination.

Transport of substances within a cell occurs
through a system of channels known as the
endoplasmic reticulum (ER).

The channel walls are formed by membranes.
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Organelles
“Endoplasmic Reticulum”
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Function
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Organelles
“Golgi Complex”

The golgi complex is prominent in cells as it allows
proteins to exit the ribosome and enter the
endoplasmic reticulum.

The golgi complex packages protein into
membrane bound bags or vesicles for export.

The vesicles then carry the material out of the cell.
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Organelles
“Golgi Complex”

Quick
Check
Questions
4-8 p35
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Function
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Organelles
Lysosomes “Controlled Destruction”

Lysosomes are membrane bound sacs containing
dissolved digestive enzymes.

Lysosomes can digest material brought into their sacs.

Lysosomes play a role in organised cell death.

The process of programmed cell death is known as
apoptosis.

Example – Embryo Fingers p36
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Organelles
Chloroplasts “Sunlight Trappers”

Chloroplasts are relatively large organelles found in
photosynthetic cells of plants and algae.

Chloroplasts have an external membrane and
layers of folded internal membranes.

Chlorophylls are located inside chloroplasts.

Chloroplasts trap energy from sunlight and convert
it to chemical energy in sugars. This is called
photosynthesis.
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Organelles
Chloroplasts “Sunlight Trappers”
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Organelles
Flagella “Whipping Around”

Some bacterial cells and other single celled
organisms have a whip like structure that is
attached to the plasma membrane and
protrudes through the cell wall.

This structure is known as a flagellum.

Vibration and rotation of the flagellum results in
the cell being able to move around.
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Organelles
Flagella “Whipping Around”
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Function
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Putting It All Together
Chapter 2 - Cells: Structure &
Function
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Animal Cells
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Function
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Plant Cells
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Function
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Cells Activities

Quick Check Questions 9-14 p42

Manual Activity – Cell Structures & Organelles
p80-81

Manual Activity – Animal Cells p85

Manual Activity – Plant Cells p84
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Levels of Organisation

Unicellular organisms must carry out all the
metabolic processes necessary for life.

In contrast, multicellular organisms have
millions of specialised cells that depend on
each other for survival.


Specialised cells in multicellular organisms are
organised into different levels so they can
perform their specific fucntions.
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Tissues

When cells that are specialised in an identical
way aggregate to perform a specific function,
they are called a tissue.

Different kinds of tissue serve different
functions in an organism.

For example, cardiac muscle is a particular
type of muscle tissue comprised solely of
cardiac cells and only found in the heart.
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Tissues
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Function
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Surface Area to Volume Ratio
(SA:V)

Both materials that enter a cell and wastes must enter
and exit the cell via the plasma membrane.

The larger the cell – the bigger the surface area for this
exchange – the more materials that can enter or exit.

But when you increase surface area – you must also
increase the volume in the cell even more.

Exchange of materials between tissues and their
environments has the potential to be far more efficient if
the tissue is made up of many small cells rather than
fewer larger cells.
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Function
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Surface Area to Volume Ratio
(SA:V)

Activity Sheet – Limitations to Cell Size p98-99
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Organs

In multicellular organisms, groups of different
tissues often work together to ensure a
particular function is successfully performed.

A collection of such tissues is called an organ.

Your stomach is an organ. It is comprised of
tissues such as epithelium (lining), smooth
muscle cells and blood.
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Organs
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Function
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Organ Systems

Activity Sheet –
Levels of Organisation
p108-109
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Function
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Chapter Review

Bio-Challenge p47

Chapter Review Questions 1-9 p48
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Function
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