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Cell Structure and Organisation Notes 2
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Cell Structure and Function
1
The cell structure of plants was first discovered by
Robert Hooke in 1665.
2
He examined fine slices of cork with a primitive
microscope.
3
He observed that the cork was actually made up of many
small compartments like bricks and separated by
partitions (Figure
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What You Will Learn
1,,1 Cell Str,ucture and Function
1.2
These compartments were named cells and the
partitions were called cell walls.
5
Robert Hooke's discovery showed that all organisms
are made up of one or more cells.
6
Hence, the cell is the basic unit or building block for all
living organisms.
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Specialised Cells,Tissues and
Organs
Figure 1.1 Cork cells
Structure of Animal Cells and Plant Gells
1
2
Cells are the basic units of life.
The function of cells is to carry out life processes such
as respiration, excretion, growth and division.
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Cell ,,
Structure and
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1.1 ).
3
4
5
6
7
8
Cells exist in various shapes and sizes.
Generally, a cell is made up of a plasma membrane
which encloses protoplasm.
Protoplasm is made up of cytoplasm and a nucleus.
The cytoplasm contains many organelles.
Organelles are specialised structures which are
surrounded by their own membranes and perform
specific functions.
Organelles that are found in animal cells include the
nucleus, rough and smooth endoplasmic reticulum,
mitochondria, Golgi apparatus, ribosomes and
vacuoles.
1
Plant cells have chloroplasts in addition to all
the organelles in animal cells.
10 Structure of an animal cell
(a) A cheek cell is an example of an animal cell,
(b) Animal cells do not have regular shapes.
(c) Each animal cell is enclosed by a plasma
membrane.
(d) Each cell has protoplasm which consists of
the cytoplasm and a nucleus.
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11 Structure of a plant cell
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(a) The epidermal cells
of an onion or cells of
hydrilla leaf are examples of plant cells.
a
(b)Each cell is enclosed by a plasma
membrane which is protected by a cell wall.
(c) Plant cells have a fixed shape because they
have cell walls.
(d) Each cell has a nucleus and cytoplasm.
(e) Plant cells have chloroplasts which contain
chlorophyll.These are present in the cells of
hydrilla leaves but not in the epidermal cells
of onions.
(f) A mature plant cell has a large vacuole
which contains cell sap.
12 Figure 1.2 shows the structure of an animal cell
and a plant cell as seen through an electron
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microscope.
plasma
nucleus membrane
nucleus
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rough endoplasmic
reticulum
ca
ribosome
cytoplasm
reticulum
mitochondria
lysosome
cell
centriole
lr-----;a
rc
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(a)
Animal
vacuole
cytoplasm
(b)
ptant ceil
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Figure 1.2 Structure of an animal cell and a plant cell
2
CONCEPT FOCUS
The cytoplasm is a jelly-like liquid surrounding the
nucleus. lt is where metabolic activities take place.
The cytoplasm together with the nucleus constitutes
protoplasm.
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EXPERIMENT
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Obiective
Prepare and study a slide of animal cells (human cheek cells)
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Apparatus and materials
Light microscope, glass slide, cover slip, long needle, toothpick, methylene
blue, filter paper
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Procedure
The inside of the cheek is scraped with a toothpick.
2
The cheek extract is placed on the slide. A drop of water is dripped on
it (Figure t.3(a)).
4
5
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water
With the help of a long needle, a cover slip is gently lowered onto the
specimen (Figure 1.3(b)).There should be no air bubbles trapped under
the cover slip.
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A drop of methylene blue solution is placed at one end of the cover
slip and a strip of filter paper is placed at the other end.The filter
paper will draw the solution across the specimen and colour it.This
technique is called the irrigation technique (Figure t.3(c)).
The slide is then observed under the light microscope using the lowpowered lens, followed by the high-powered lens.
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Observation
t
cytoplasm
\-
,
T
distilled
1
C)
slide
(a)
long needle
slip
(b)
methyle
blue
(c)
Figure 1.3 Preparing slide
of human cheek cells
plasma membrane
ure 1.4 Human cheek cells
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Conclusion
The human cheek cells are not regular in size or shape. Each human cheek
cell contains a nucleus, cytoplasm and plasma membrane.
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Objective
Prepare and study a slide of plant cells (epidermal cells of onion and cells of hydrilla)
Apparatus and materials
Light microscope, glass slide, cover slip, razor blade, long needle, dropper, forceps,
filter paper, iodine solution, big onion, hydrilla plant, distilled water
3
Procedure
1 A leaf from a bulb of an'onion is peeled off (Figure 1.5(a)).
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An epidermal layer from the leaf is peeled with a razor blade.
drop of
distilled
The epidermal layer is then placed on the glass slide that
alreadv has a droo of water on it (Fioure r.itOtt
(a)
A cover slip is placed at an angle over the water droplet
on the slide and gently lowered to cover the specimen
without trapping any air bubbles (Figure t.5(c)).
(b)
, long
>--Qi
needle
---4\(
5
The slide is observed under a microscope starting with the
low-powered lens, followed by the high-powered lens.
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6
A drop of iodine solution is added to one end of the cover
slip and allowed to seep beneath the cover slip.
cover slip
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A strip of filter paper is placed at the other end of the cover
slip to absorb any excess iodine and water (Figure 1.5(d)).
8
The slide is observed under the microscope again, first on low
magnification, then on high magnification.
9
The structure of the onion cell is drawn.
Observation
cytoplasm
nucleus
cell wall
membrane
Figure 1.6 Epi dermal cells of
Figure
chloroplast
cell wall
plasma membrane
cytoplasm
nucleus
vacuole
vacuole
onion
Figure 1.7 Cells of hydrilla leaf
Conelusion
Plant cells have a regular shape. All plant cells contain a nucleus, cell wall,
4
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plasma membrane, cytoplasm and a big vacuole. Epidermal cells of the
onion do not contain chloroplasts while the cells of hydrilla leaves contain
ch
Ioroplasts.
(d)
1.5
Preparing slide of
onion cells
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10 The experiment is repeated using a hydrilla leaf
(c)
filter paper
solution
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7
water
leaf
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2
3
epidermal layer
epidermis
of onion
Functions of Cellular Components
Cellular component
N
o
Structure
Function(sl
Plasma membrane
.
Thin, semi-permeable membrane
r
Cell wall
.
Thick layer outside the plasma
o
Maintains the shape of the plant
o
cells
Provides support for plant body
.
Acts as a medium for metabolic
N
o
membrane
R
o Made up of cellulose and fully
G
Controls the movement of
substances in and out of the cell
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G
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o-
permeable
A
N
.
Cytoplasm
L
.
L
E
Jelly-like substance that contains
water and mineral salts
Contains organelles
S
.
.
Small particle consisting of RNA
(ribonucleic acid)
Exists freely in the cytoplasm or on
the surface of the rough
endoplasmic reticulum
Ribosome
o
Rough and smooth endoplasmic
reticulum
A
N
.
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R
G
.
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L
endoplasmic
reticulum
.
o
Controls and regulates all the
activities of the cell
Contains the hereditary factors
(genes) responsible for the traits
of the animal or plant
o
Synthesis of protein
o
Transport system for protein and
lipids within the cell
Rough endoplasmic reticulum
transports the protein
synthesised by the ribosomes to
other parts of the cell
Smooth endoplasmic reticulum
stimulates the synthesis of lipids
and cholesterol and transports
them within the cell
.
.
rough
endoplasmic
reticulum
o
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Mitochondrion
A system of membrane-enclosed
tubules closely packed together
and continuous with the nuclear
membrane
Rough endoplasmic reticulum has
ribosomes while the smooth
endoplasmic reticulum does not
have ribosomes
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s
Spherical with a double membrane
Contains nucleolus, chromosomes,
nucleoplasm and nuclear
membrane
reactions
Supplies the substances required
by the organelles
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Nucleus
.
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outer membrane
inner membrane
membrane
Outer membrane is smooth and
regulal the inner membrane is
folded to form cristae
.
o
Known as the 'power-house' of
the cell
Releases energy as it is the site
for aerobic respiration
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crista
o
Rod-shaped with a double
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Function{s}
Structure
Cellular component
.
Golgi apparatus
Vacuolar region surrounded by
complex meshwork of vesicles
budding off at its end
.
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Golgi apparatus
secretory
vesicle
cells
o
r
.
Disc-shaped organelle with
.
a
double membrane
Consist of an orderly arrangement
of grana within the stroma
Each granum contains chlorophyll
stroma granum
tonoplast
CONCEPT FOCUS
Carries out photosynthesis
Cavities filled with cell sap
surrounded by a semi-permeable
membrane called the tonoplast
Contains water, sugar and
dissolved minerals
Maintains turgidity of cells in
plants
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Vacuole
nucleus
Controls the secretory activity of
o Formation of lysosomes
Chloroplast
cytoplasm
be secreted
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o
modifies them to form specific
secretions such as enzymes and
hormones
Packs the secretions formed Into
secretory vesicles and transports
them to the plasma membrane to
ion
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Receives protein and lipids from
endoplasmic reticulum and
Animal cell
Difierences
Plant cell
No fixed shape
Shape
Fixed shape
Organelles are subcellular structures found in the
cytoplasm, each with a specific functional role in the cell.
Comparison Between the Structure of an
Animal Gell and a Plant Gell
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Plant cell
Similarilles
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Both have a plasma membrane, cytoplasm, a nucleus,
mitochondria, Golgi apparatus and endoplasmic reticulum
6
Does not have
a
cell wall
Cell wall
Does not have
ch loro p lasts
Usually has
numerous small
Vacuole
vacuoles
Contains
glycogen
g ra nu
les
Granules
Has a cellulose
cell wall
Has chloroplasts
which contain
chlorophyll
Usually has a
large vacuole
Contains starch
g
ranules
Understanding key ideas
Tick
1
(/)
1
if the statement is true.
The cell is the basic unit of life for all
organisms.
2
Plant cells have a plasma membrane,
2
The nucleus consists of chromosomes
and a nucleolus.
Organelles that are found in the
cytoplasm of a cell include the nucleus,
vacuole, endoplasmic reticulum,
mitochondria and Golgi apparatus.
5
The vacuole of a plant cell is enclosed
by the tonoplast.
6
Human cheek cells and epidermal cells
of onions do not have chloroplasts.
7
Epidermal cells of onions have small
vacuoles.
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tl
State the components of cells which carry out
the following functions.
(a) Contains a pigment which absorbs energy
from sunlight for photosynthesis
(b) Site for generating energy
(c) Controls the movement of substances going
in and out of the cell
(d)An organelle which contains the hereditary
factors called genes
(e) Helps to keep the cell turgid
(f) Has ribosomes on it to synthesise protein
(g) Provides support and shape to the cell
(h) Receives organic molecules and packages
them to form specific secretions
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Give three differences between human cheek
cells and the epidermal cells of an onion.
3
Suggest why sperm cells have a high density
of mitochondria while the human cheek cells
have only a few mitochondria.
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Each multicellular organism is organised as
follows:
cell ) tissue
organ system
)
)
organ )
organism
Cell
1
Cells are the basic units of life in all organisms.
2
The structural features of cells are related to
their functions.
3
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Main concepts and facts
3
4
Cells undergo differentiation to acquire special
structures and become specialised cells with
specific functions.
The following describe the various types of
cells with their specific functions.
(a) Root hair cells
(i) The functions of the roots are to anchor
the plant to the soil and to absorb water
from the soil.
Root hairs are outgrowths of the
epidermal cells.
(iii) They help to increase the surface area and
thus increase the absorption of water and
mineral salts.
(ii)
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The organisation of cells allows every part of
multicellular organism to perform various
fu nctions efficiently.
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cell.
nucleus and cytoplasm.
3
ln general, organisms are divided into
unicellular organisms with single cells and
multicellular organisms with more than one
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Specialised Cells,
Tissues and Organs
1.2
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hair
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Figure 1.8 A root hair
7
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a.
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(ii) The red blood cells contain
haemoglobin. This combines readily
with oxygen to form oxyhaemoglobin.
(iii) Red blood cells are flat and biconcave in
shape to increase the surface area for
gas exchange.
(iv) Red blood cells do not have a nucleus
and can fold easily.This allows them to
squeeze through the blood capillaries.
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(c) Red blood cells
(i) The function of the red blood cells is to
transport oxygen all around the body.
(b)Xylem vessels
(i) The functions of the xylem vessels are
to conduct water and mineral salts from
the roots to the leaves and to provide
support to the plant.
(ii) Xylem vessels are non-living, i.e. they
do not contain protoplasm and so are
hollow.
(iii) The vessels are placed end to end to
form a continuous tube for passage of
water and mineral salts.
(iv) The vessels are thickened with lignin to
provide strength and support to the
pe.
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Plant.
Figure 1.10 Red blood cells
Tissue
Figure 1.9 Xylem vessels
Trpe ol animal tissue
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Epithelium lining of skin
(ii)
Epithelium lining of blood capillary
(b) Nervous tissue
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(i)
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Examples: sensory neurone, motor neurone,
intermediate neurone
cell body
8
work together to perform a specific function.
axon terminal
There are four main types of animal tissues:
epithelial tissue, nervous tissue, muscle tissue
and connective tissue.
Characteristic{s}, and f unction{s}
o
(a) Epithelial tissue
A tissue is defined as a group of similar cells that
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1
.
Consists of epithelial cells arranged in a continuous
layer
Covers the body surface (exterior) or lines the cavities
within the body
o
Protects the underlying cells from mechanical inlury
Acts to absorb food and water by diffusion
.
.
Consists of nerve cells called neurones
Sends and receives impulses to coordinate the activities
.
of the body
Found in the brain and spinal cord
Type of animal tissue
Characteristic{s} and lunction{s}
o
(c) Muscle tissue
cardiac
o
Consists of muscle cells which can contract to perform
work and cause body movement
Three types of muscle tissue: smooth muscle, skeletal
muscle and cardiac muscle
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(ii)
Smooth muscle in
the walls of ileum
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Cardiac muscle
of the heart
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or stomach
Connective tissue
o
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OGB
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(i)
Blood
.
.
Consists of elastic and non-elastic fibres
Joins together body structures, as well as protects,
holds and supports the cells in the body
Can store and transport materials
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(i)
(iii)
Cartilage
(iv)
Bone
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(ii) Adipose tissue
CONCEPT FOCUS
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Tissues are made up of the same type of cells which carry out a special function. Some types of tissues contain
several types of cells, but the whole tissue performs one function. Connective tissue, for example, connects
different parts of an organ or organs together.This kind of tissue is called complex tissue.
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Examples of plant tissues are epidermal tissue, meristematic tissue and vascular tissue
'Charaaeristic(s}' and lunction{s}
Type'of plant tissue
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(a) Epidermal tissue
stoma
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,
.
Examples: epidermis of leaves, stems and roots
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Consists of one layer of cells
o Covers the entire surface of the plant
'l o Protects underlying tissues from physical damage and
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.
infection
Reduces water loss
Epidermal cells of leaf differentiate to become guard cells
while those at the root become root hair cells
.
'.
(b) Meristematic tissue
nucleus
Consists of undifferentiated cells which are able to divide
Occurs at the tip of roots and shoots (apical meristem)
and in the cambium of stems and roots (lateral
meristem)
Examples: apical meristem of root and shoot, cambium
in the stem
.
Vascular tissue
o
xylem
vessels
phloem
Examples: xylem, phloem
Each organ in an animal is formed from the
four main types of animal tissues. All these
tissues work together to perform a specific
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fu nction.
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Examples of organs in animals are the heart,
stomach, skin, kidneys and lungs.
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A group of different tissues that work together
to perform a specific function is called an
o rga n.
2
Consists of xylem tissues and phloem tissues
Transports water and mineral salts from roots to the
stems and leaves by xylem tissues
Transports dissolved nutrients such as sugars from the
leaves to the roots and stems by phloem tissues
Xylem tissues also provide support to the plants
7
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1
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(c)
ion
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For example, the heart is an organ made up of
epithelial tissue, muscle tissue, nervous tissue
and connective tissue to pump blood to all
parts of the body.
5
Examples of organs in plants are leaves, stems,
roots and flowers.
6
The leaf of a plant is made up of epidermal
tissue, vascular tissue and mesophyll tissue to
ca rry out photosYnthesis.
Certain organs perform more than one
function. For example, the liver can convert
excess glucose to glycogen as well as secrete
bile.
CONCEPT FOCUS
An organ, such as the stomach or liver, is a structure made
up of different types of tissues working together to perform
a function. For example, the stomach is made up of four
types of tissues
-
glandular tissue, muscle tissue,
connective tissue and nervous tissue.
0rgan System
1
2
Several organs which work together to carry out
a specific function form an organ system.
The human body has different systems, each
performing a specific function in the body
(Figure 1.11).
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mouth
salivary
glandsoesophagus
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heart
liver
caecum
rectum
anus
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stomach
pancreas
ileum
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multicellular
organrsm
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organ
w
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ion
system
Figure 1.12 An organism
(b) Digestive system (Breaks
down food into simple
substances so that they
can be absorbed by the cells)
CHECK
A
1
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Figure 1.11 Different types of systems in the human
body
3
Each system consists of a few organs made up
of various tissues.
4
For example, the digestive system consists of
the mouth, oesophagus, stomach, ileum,
duodenum and large intestine.
5
if the statement is true.
Cell specialisation allows cells to
form tissues.
2
Tissues are organised into functional
units called organs.
3
The stomach, small intestine, liver and
pancreas work together as parts of the
digestive system which is required for the
intake, digestion and absorption of food.
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nerves
(c) Nervous system (Conducts impulses
around the body and coordinates
activities in the body)
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spinal
cord
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Understanding key ideas
Tick
brain
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(a) Blood circulatory system
(Transports food
substances and oxygen
around the body)
All the organ systems work together to form an
organism (Figure 1.12).
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A flowering plant has two main systems: a root
system and a shoot system.
7
The shoot system consists of the stem, leaves,
buds, flowers and fruit while the root system
consists of the tap roots and lateral roots.
4
Root hair cells are long and narrow to
increase the surface area for the
absorption of water and mineral salts.
B
1
Main concepts and facts
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Red blood cells contain
which enables them to transport oxygen from
the lungs to the tissues.
2
A root hair is an example of
3
The stomach is an example of an organ
because
do not have
4
a
nucleus and can fold easily.
5
Xylem vessels are adapted to conduct water
and mineral salts from roots to leaves because
11
6
Fill in the blanks in the concept map with the
words given to show the levels of organisation
in animals.
Word list
F
Organs
Cartilage
Muscle
E.
Kidney
Brain
Tissues
Organism
Reproductive
Homo sapien
Liver
Systems
Bone
Excretory
Endocrine
Cells
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such as
such as
form
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such as
form
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such as
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CELL STRUCTURE AND ORGANISATION
Function
Nucleus
Controls all cell activities
Endoplasmic reticulum- Transports proteins, lipids and glycerol
Mitochondria
Produce energy
II
I
I Cof Si apparatus
I Ribosome
Chloroplasts
t
Cell
Plasma membrane
Non-
kp:l:lle,
t
o
Controls secretory activity of the cell
Synthesise protein
Carry out photosynthesis
Contain cell sap
Vacuoles
-
Cytoplasm
Cell wall
Controls flow of materials in and
out of cell
Medium for chemical processes
Gives shape, support and protection
to cell
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tlu*99
Plant cells
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Unicellular
Types of organisms
Multicellular
Cell specialisation
Cell organisation
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Cells with specific
structu res and functions
(Root hair cells, xylem
vessels, red blood cells)
l'issues
Organs
Nervous Muscle
Connective
I'IN
Stomach Brain Heart
tlll Nervous Circulatory
Digestive
system system system
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Systems
Epithelial
Plants
Animals
Epidermal
Vascular
Meristematic
Stem
'
Root
'
Transport
system
Root
system
r
Bone
Leaf
I
Skeletal
system
Foodmaking
system
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Structure
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Organelles
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