Download Chap 2 - CRCBiologyY11

Unit 1 Biology
Chapter 2
Structure and function of cells
Key knowledge
This chapter is designed to enable students to:
 Investigate the defining characteristics of prokaryotic and
eukaryotic cells
 Identify cell structure and organisation
 Identify cell organelles and understand their function
 Investigate the different modes of transport of materials
across plasma membranes
 Understand and apply the principal of surface area to volume
ratio
Looking at cells
All cells are similar in some ways:
• Each cell is a small compartment surrounded by a cell
membrane, which holds in the fluid (cytosol) that the
organelles float around in.
• All cells also have DNA in some form inside of them, that
carries their genetic material.
But cells can also differ greatly. Living cells can be classified
into two groups based on differences of their internal
structure:
• Prokaryotic cells – very basic internal structure with no
membrane-bound nucleus (e.g. bacterial cells)
• Eukaryotic cells – more complex internally, with membranebound organelles, including a nucleus (e.g. animal cells)
Cells vary in size
Prokaryotes vs eukaryotes
Characteristics of living things
Animal cells
Plant cells
Biological drawings
A biological drawing of an animal
cell
A biological drawing of a plant cell
Draw up a table to show which organelles are:
a) Only present in plant cells
b) only present in animal cells
and
c) present in both animal and plant cells
The plasma membrane
• Present in all living cells both eukaryotic and prokaryotic.
• Controls the movement of dissolved substances in and out of
the cell, therefore maintaining the internal environment of the
cell.
• It is made up of protein and lipid (fat) molecules.
• A model designed to describe the appearance of the plasma
membrane is shown below
Proteins of the plasma membrane
Movement in and out of cells
• All cells need to be able to take in and expel various
substances across their cell membrane in order to survive,
grow and reproduce.
• Because the membrane (m/b) only allows some substances
to pass through, it is called partially permeable
• Dissolved substances can cross the plasma m/b in a number
of ways:
- Diffusion
- Osmosis
require no energy
- Active transport
- Bulk transport
requires energy
Diffusion
• A way that substances move into and out of cells, that
requires no energy by the cell.
• Movement is from a region of high concentration of that
solute to a region of low concentration for that solute,
through a semi-permeable membrane.
• Refer to Fig 2.7
• Movement will continue until the concentration of the solute
on both the inside and the outside are equal.
Osmosis
• Osmosis is a special type of diffusion – it involves water
• So, osmosis is the movement of water across a semi
permeable membrane from a region where it is at a high
concentration, to a region where is at low concentration.
• Osmosis can result in cells lysing (bursting) or shrinking
depending on the solution they are in.
• Refer to the blue box of information on p28.
• E.g. Freshwater fish do not need to drink, they rely on
osmosis to get their water. Over what surface might the fish
obtain their water?
Active transport
• AT is another way in which substances can move into and
out of cells
• Different to diffusion and osmosis in that it requires energy
from the cell in the form of adenosine triphosphate (ATP
• Movement of molecules is the opposite to that in diffusion –
molecules move from a region of low concentration to a
region of high concentration
• Refer to figure 2.9 b
• In comparing diffusion to active transport we use the slippery
slide model
- going up the slippery slide (concentration gradient) requires
energy
- going down the slippery slide does not require energy
Facilitated diffusion
• This special type of diffusion that requires energy.
• This occurs as some substances cannot dissolve through the
plasma membrane to cross it.
• These molecules are carried through the protein channels by
special molecules called carrier proteins.
• The inherited disorder cystic fibrosis results from a defective
carrier protein that is meant to transport chloride ions into the
cell
Bulk transport - Exocytosis
•
Particles can also be moved into and out of cells via bulk
transport.
• Exosytosis is the bulk transport of substances out of a cell.
It involves:
1. a vesicle forming around the particles that need to be
moved out,
2. the vesicle moves up to and fuses with the cell membrane,
3. the lipid bilayer opens up and moves the contents of the
vesicle out of the cell
• Refer to Fig 2.13
Bulk transport - Endocytosis
• Endocytosis is the bulk transport of substances into a cell.
• Endocytosis can involve the bulk transport of:
a) Solids – called phagocytosis
b) Liquids – called pinocytosis
It involves:
1. A cleavage forming in the lipid bilayer and the particles
moving into that,.
2. the cell membrane coming together to form a lisosome
3. The lisosome breaking off from the membrane and then
dissolving the particles inside it with digestive enzymes
Only some cells (white blood cells and single celled organisms)
are capable of phagocytosis, whereas most cells are
capable of pinocytosis.
• Refer to Fig 2.11 and 2.12
Cell walls
• Present in prokaryotes, plants and fungi.
• Semi-rigid, protective structure that lies outside the cell m/b.
• Composition varies depending on organism group:
- plants: cellulose
- fungi: chitin
- bacteria: complex polysaccharides
Cell organelles
We will be looking at the structure and function of the following
organelles in detail:
• Nucleus
(control centre)
• Mitochondria
(energy supply)
• Ribosomes
(protein makers)
• Endoplasmic reticulum
(transport systems)
• Golgi complex
• Lysosomes
(controlled distruction)
• Chloroplasts
(sunlight trappers)
• We will also briefly look at vacuoles, cilia, peroxisomes,
endosomes and vacuoles.
Nucleus
• Present in eukaryotes and encloses the DNA.
• Absent in prokaryotes, DNA is dispersed throughout cell.
• The nucleus is often referred to as the control centre of the
cell, as the DNA (held in the nucleus) is responsible for all of
the cells activities, including:
- reproduction, instruction ribosomes to
manufacture protein, cell death.
• DNA is the abbreviation for
deoxyrobonucleic acid.
• Some specialised cells in the body
have no nucleus (red blood cells) while
others (liver cells) have two.
Mitochondria
• Provide the cell with the energy
it requires to carry out all of
its functions.
• Only present in eukaryotes.
• The form of energy used by the cell
is adenosine triphosphate (ATP)
• ATP is manufactured in the
mitochondria by a chemical process
known as cellular respiration, the
equation for which is shown below:
Ribosomes
• Ribosomes are the site at which all of the protein required by
the cell is synthesised (made).
• Ribosomes are present in both eukaryotes and prokaryotes,
and are so small that they can only be seen with an electron
microscope.
• The protein synthesised by the cell depends on the
specialised function of that cell, for example
- Red blood cells make haemoglobin
- Pancreas cell make insulin
- Liver cells make protein enzymes, like catalase
- Stomach cells make digestive enzymes
- Muscle cells make contractile proteins, actin and myosin
Endoplasmic reticulum and Golgi complex
• These are two different organelles, but they are often
referred to together.
• This is because they work together inside the cell, to make
up the cell transport system, whether that be within the cell
or out of the cell as to be transported around the body.
• Endoplasmic reticulum (ER) transports substances within the
cell, and includes smooth ER and rough ER (has ribosomes
attached – for protein transport).
• The Golgi complex (also called Golgi body or Golgi
apparatus) is a prominent feature of cells that make a lot of
protein, as its role is to transport protein out of the cell.
Refer to Fig 2.16 and 2.17
Lysosomes
• Present in eukaryotes, absent in prokaryotes.
• Sac-like structures, surrounded by a membrane and filled
with fluid which contains dissolved digestive enzymes.
• Can release these enzymes within the cell, resulting in cell
death.
• Programmed cell death like this is called apoptosis.
• Important for:
- cells that have a limited life span (e.g. cells that form the
webbing between fingers of an early human embryo)
Refer to Fig 2.18 and 2.19
- digesting unwanted materials within cells
Chloroplasts
• Specialised organelles only found
in plant cells.
• Made from a series of membranes
which form layers called grana.
• Filled with a fluid called stroma.
• Chloroplasts are green in appearance
due to the presence of light trapping pigment called chlorophyll.
• Chlorophyll is one of the key components of the chemical
process known as photosynthesis (see equation below) – the
means by which plants use the energy from the Sun to make
their own glucose.
Other organelles
• Vacuoles – large fluid-filled sacs, mainly found in plant cells
or single celled animals. Contain water and some dissolved
solutes, can have a contractile mechanism to help pump
water out of some freshwater protists.
• Endosomes – involved with endocytosis in animal cells, pass
newly ingested material to lysosomes for digestion.
• Peroxisomes – rich in enzymes that detoxify various toxic
materials that enter the bloodstream of animals.
• Cilia – found in some single celled eukaryotes, whip like
structures formed by extensions of the plasma membrane
involved in synchronised movement.
• Flagellum - whip like structure found in some
eukaryotic organisms and some bacteria involved
in movement.
Levels of organisation
• Multicellular organisms, as the name suggests are made of
many cells.
• When an organisms is made up of more than one cell, its
‘body’ has different levels of organisation.
Cells
Tissues
Organs
Organ systems
Organism
Chapter Questions
• Quick-check questions
- 1-3 p31
- 4-8 p35
- 9-14 p42
- 15-16 p46
• Chapter review questions