CHAPTER 2

Cells
 Learning Outcomes

Candidates should be able to:

(a) identify cell structures (including organelles) of typical plant and

animal cells from diagrams, photomicrographs and as seen
under the light microscope using prepared slides and fresh
material treated with an appropriate temporary staining technique:

• chloroplasts
• cell membrane
• cell wall
• cytoplasm
• cell vacuoles (large, sap-filled in plant cells, small, temporary in
animal cells)
• nucleus
 Learning Outcomes

Candidates should be able to:

(b) identify the following organelles from diagrams and

electronmicrographs:
• mitochondria
Image of cells under
• ribosomes microscope
Structure of the cell

(c) state the functions of the organelles identified above

(d) compare the structure of typical animal and plant cells

 Learning Outcomes

Candidates should be able to:

(e) state, in simple terms, the relationship between cell function

and cell structure for the following:

• absorption – root hair cells

• conduction and support – xylem vessels
• transport of oxygen – red blood cells

(f) differentiate cell, tissue, organ and organ system

Use the knowledge gained in this section in new situations or to

solve related problems.
CELLS
 Cells
What are they?

• Cells are the building blocks of life.

• Many chemical reactions occur in the cell.

Number of cells in humans?

37, 200, 000, 000, 000

 Cells
How small are they?
 Cells
Then how do we see them?

How can we study the parts of the cell?

Most cells are too small to be seen.
• We can use light and electron microscopes to see the
cells and their parts.

Cameras can fitted to

the microscope to take
pictures called
micrographs.

What Hooke probably saw

 Viewing cells
2 ways of sectioning cells - Longitudinal

Cutting along the length of the cucumber

 Viewing cells
2 ways of sectioning cells - Longitudinal

Viewing cells from different perspectives

Longitudinal section

Cutting along the length of the cell

 Viewing cells
2 ways of sectioning cells - Transverse
(Cross-section)

Cutting across the length of the cucumber

 Viewing cells
2 ways of sectioning cells - Transverse

Viewing cells from different perspectives

Transverse section

Cutting across the length of the cell

 Viewing cells
2 types of cells

Plant cell Animal cell

cytoplasm

nucleus

cell
membrane

cell wall
Structures found inside a cell
 Organelles
1. Cell surface membrane

cell surface membrane

• Also known as plasma membrane.
• It is partially permeable. Semi-permeable
- It controls the substances
entering or leaving the cell.

Allow small substances to

enter / leave but not the large
ones
 Organelles
2. Cytoplasm

cytoplasm Main reaction region of the cell

• Most cell activities occur here.

• It contains specialised structures
called organelles.
Jelly-like substance
 Organelles
3. Nucleus

• Nucleus To make more cells for growth and repair

- controls the activities of
the cell.
- essential for cell division.
- contains the inherited chromatin
genetic material of the cell
(DNA) [found in chromatin] nucleus

Contains ‘instructions’ that determine characteristics

Deoxyribonucleic acid stands for DNA

 Organelles
3. Nucleus - Chromatin
• Chromatin is found inside the nucleus
• Chromatin is a network of threadlike structures that controls cell
activities like cell division.
• Chromatin is made of deoxyribonucleic acid or DNA that stores
hereditary information.
• Chromatin threads condense into chromosomes when the cell is
actively dividing.

chromatin

Diagram showing
parts of a nucleus
Two cells are shown. Which structure contains a large amount of
heritable material?

SciBio 2009 P1Q21

The diagram shows part of a plant cell. Which part controls the entry
of substances into the cell?

SciBio 2012 P1Q21

 Organelles
4. Vacuole (animal cell)

Vacuole (animal cell)

• Stores substances within cell.
• Animal cells have many vacuoles
containing water and food
substances.

animal cell under an

electron microscope
 Organelles
4. Vacuole (plant cell)

Vacuole (plant cell)

• Stores substances within cell.
• Plant cells have a large central
vacuole containing cell sap (made up
of sugars, mineral salts and amino
acids).

Tonoplast (Membrane)
plant cell under an
• Surrounds the large vacuole
electron microscope
 Organelles
5. Cell wall (PLANT ONLY!!)

Cell wall:
•Made of cellulose
•Functions:
- It protects the cell from injuries.
- Maintains shape of the cell.
- It is fully permeable.
•Cell wall is absent in animal cells.
 Organelles
6. Chloroplast (PLANT ONLY!!)

Chloroplast
• contains chlorophyll (green pigment)
that traps sunlight for plants to make
food.

plant cell under an

electron microscope
 Organelles
7. Ribosome

Ribosome
• Ribosomes are either free or attached
to membranes.
• They are needed to synthesise /make
proteins for the cell.

animal cell under an

electron microscope
 Organelles
8. Mitochondrion ENERGY

Mitochondrion
• Performs aerobic
respiration.
- Oxidises glucose
(breaks down glucose in Sweet bananas are
presence of oxygen) to rich in glucose
release energy.

animal cell under an

electron microscope Mitochondrion (singular)
Mitochondria (plural)
Which diagram shows a mitochondrion?

SciBio 2015 P1Q21

Which labelled structure produces carbon dioxide?

SciBio 2016 P1Q21

 Cell structure & organisation
Comparing between plant & animal cell

Plant cell Animal Cell

Cell wall present Cell wall absent

Chloroplast present Chloroplast absent

A large central vacuole Small and numerous

vacuoles

Similarities:
Nucleus, cytoplasm, cell surface membrane, mitochondria
and ribosome present
 Specialised cells
Differentiation
E.g liver cell - a few specific

Specialised cell functions

• There are many specialised cells in organisms

- Process for this development is called differentiation.

Differentiation is the process by which a cell

becomes specialised for a specific function.

• 3 specialised cells you need to know

• Red blood cell Brain cell: performs a different function
from a brain cell
• Xylem vessel Function: process nervous impulses and
• Root hair cell interpret information
 Specialised cells
Differentiation
 Specialised cells
1. Red blood cell
Binds to oxygen

(Pigment)
• Haemoglobin in cytoplasm
of red blood cells transports
oxygen from lungs to all
parts of the body.
• A red blood cell has no
nucleus, enabling it to load
cytoplasm contains
more oxygen.
haemoglobin
 Specialised cells
1. Red blood cell

• A red blood cell has a

biconcave shape (thinner
central portion)
– increasing the surface
area to volume ratio.
– Oxygen can thus diffuse
thinner central in and out more
portions efficiently.
Which description applies to a red blood cell?

SciBio 2007 P1Q22

 Specialised cells
2. Xylem vessel

lumen
lignified • Xylem vessels do not
wall
have cross walls or
protoplasm.
– This enables water and
mineral salts to move
through the lumen
pits Transverse easily.
Section.

Xylem vessel
 Specialised cells
2. Xylem vessel

• A substance called lignin

is deposited in xylem
lignin
vessels.
– Lignin strengthens the
xylem walls and
prevents the xylem from
collapsing.
– Xylem also provides
lignin mechanical support for
the plant.
 Specialised cells
3. Root hair cell

• It has no chloroplasts as
it does not
photosynthesise.
• A root hair cell has an
extension that is long and
narrow.
– This increases the
long and narrow surface area to volume
root hair cell ratio to absorb water
and mineral salts
efficiently.
Which structure indicates that a root hair cell is from a
plant and not from an animal?

SciBio 2009 P1Q21

 Multicellular organisms
Organisation of cells

Cells Specialised for a particular

function

A group of similar cells which

Tissue work together to perform a
specific function

Organ Different tissues working together

to carry out a specific function

Several related organs working

Organ system together to carry out a particular
function
 Multicellular organisms
Cell  tissue  organ  organ system

Tissues
• A group of cells working together is called a tissue.

A tissue is a group of cells with similar structures

which work together to perform a specific
function. There are two types of tissues: simple
tissue and complex tissue.
 Multicellular organisms
Cell  tissue  organ  organ system

Simple tissues in animals

•Simple tissues are made up of only one type of
cells.
•Examples include epithelial tissue and muscle
tissue.

Muscle tissue
 Multicellular organisms
Cell  tissue  organ  organ system

Simple tissues in plants

• Examples include the epidermis.
 Multicellular organisms
Cell  tissue  organ  organ system

Complex tissues in animals

•Tissues with different cell types are called complex
tissues.
•Examples include connective tissue, nervous tissue,
glandular tissue and bone tissue.
 Multicellular organisms
Cell  tissue  organ  organ system

Complex tissues in plants

•Examples include vascular tissue.
 Multicellular organisms
Cell  tissue  organ  organ system

Organs
•Different tissues may combine to form an organ to
perform a specific function.

An organ is a group of tissues which work

together to perform a specific function.
 Multicellular organisms
Cell  tissue  organ  organ system

Organs in animals
•An example is the
stomach. It is made up of
many tissues and its
function is to digest food.
 Multicellular organisms
Cell  tissue  organ  organ system

Organs in plants
•An example is a leaf. It is made
up of several tissues, and its
function is to photosynthesise.
 3

2
1

4
The diagram shows the
structure of a cell. Which
identifies a cell, a tissue and
an organ?

SciBio 2011 P1Q21 & 2010 P1Q22

 Multicellular organisms
Cell  tissue  organ  organ system

Organ systems
•Different organs work together to form an organ
system.

An organ system is a group of organs which

work together to perform a specific function.
 Multicellular organisms
Cell  tissue  organ  organ system

Organs work together to form organ systems

trachea
stomach
(organ)
(organ) digestive respiratory
system system

lungs
intestine (organ)
(organ)
 Multicellular organisms
Cell  tissue  organ  organ system

Organs work together to form organ systems

 Multicellular organisms
Cell  tissue  organ  organ system
The photomicrograph shows part of an onion
epidermis. Which term describes this onion
epidermis?

SciBio 2013 P1Q21

The diagram shows a plant. Which correctly identifies P, Q
and R?
SciBio 2015 P1Q22 &
2012 P1Q22
The diagram shows a plant cell. Which numbers show
the parts named?

SciBio 2007 P1Q21 &

2013 P1Q21
The diagram shows a plant cell and some of the structures
found in it. Which structure is a mitochondrion?

SciBio 2014 P1Q21

The electronmicrograph shows part of a plant tissue. Which
structure is a partially permeable membrane?

SciBio 2010 P1Q21

The diagram shows a plant cell. Which energy
conversion happens in structure X?

SciBio 2014 P1Q27