1 edexcel igcse human biology -cell and tissues

Cambridge IGCSE Biology
1. Cells and tissues
Biology
Edexcel international GCSE
Human Biology

1- cells and tissues
a) Recognise cell structures as seen with a light
microscope and with an electron microscope.
Describe the functions of cell structures including
1- the nucleus,
2- cytoplasm,
3- cell membrane,
4- mitochondria,
5- endoplasmic reticulum,
6- ribosomes.

Under an electron microscope parts of the animal cell
such as
the ribosomes,
Endoplasmic reticulum
mitochondria
can be seen.
The main differences between a plant cell and
an animal one is the lack of certain organelles such
as a permanent vacuole, cell wall and chloroplasts.
Apart from this plant cells also have a more regular
structure.

The Functions of the parts of the cell:
1- Nucleus:
contains chromosomes (46 in humans) which carry
the genetic information. It controls the activity of the cell by controlling
which proteins the cell will synthesis.
2- Cytoplasm:
this is where chemical reactions take place .
3- Cell membrane:
this controls what substances can pass in and out of the cell. It is
selectively permeable.

The Functions of the parts of the cell:
4- Mitochondria :
this carries out some of the reactions in respiration.
Cell membrane: this controls what substances can pass in and out
5-Endoplasmic reticulum:
an essential component in the synthesis and transport of protein. It is a
network of membranes.. It is selectively
Ribosomes: some endoplasmic reticulum are covered with minute granules
6-Ribosomes: some endoplasmic reticulum are covered with minute
granules called ribosomes. These build and assemble proteins according to
instructions from mRNA.

b) Describe a DNA molecule as two strands coiled
to form a double helix,
the strands being linked by a series of
paired bases:
adenine (A) with thymine (T),
and cytosine (C) with guanine (G).
according to instructions from mRNA.

DNA or deoxyribonucleic acid contains
two strands of alternating sugar and phosphate groups
coiled to form a double helix.
The strands are linked by two nitrogen bases at each
"rung". There are four different bases:
Adenine(A), Thymine(T), Cytosine(C), and Guanine(G).
In DNA the bases are always paired.
So if on one strand the base is A, the other must be T
and likewise if on one strand it is C then on the other it
must be G..

c) Understand the multiplication of cells with a
simple outline description of the four stages of
mitosis.
Understand that division of a diploid cell by mitosis
produces two cells that contain identical sets of
chromosomes.
Understand that mitosis occurs during
growth, repair , cloning and asexual reproduction.

Mitosis:
Mitosis is a process of separating a cell into two with identical
sets of chromosomes.
This occursduring growth, repair, cloning and asexual
reproduction.
1. Prophase - the cell duplicates its DNA.
2. Metaphase - the centrioles (duplicated DNA) align
themselves along the equator (middle) and
send out tubules that connects to the centromere and connects
the two strands of chromosomes (condensed DNA).
3. Anaphase - half of the chromosomes are pulled one way
and vice versa.
4. Telophase - cell membranes closes in and splits the cell..

d) Understand the grouping of cells into tissues:
1- bone,
2- muscle (voluntary, involuntary and cardiac),
3- blood,
4- nervous tissue
5- epithelium
(squamous ( scale like ) and ciliated, with reference to
cells lining the cheek and trachea).
e) Recall the organization of cells into organs.

There are many types of tissues:
1.Bones
are collection of cells that secrete calcium salts.
2. Muscle
these can be voluntary, involuntary or also cardiac
3. Blood
collection of red and white blood cells.
4. Nervous tissue
makes up the brain, nerves and spinal cord.
5. Epithelium these are tissues that line organs.
They can be both squamous or ciliated.

1- Tissues that perform the same function are
grouped together to form organs. e.g. Heart.
2- Organs that perform the same function are grouped
together to form organ systems.
e.g. The circulation system
3- Organ systems are grouped together to form
organisms. e.g. Humans.

1 life style, health and risk
Bonds between Water molecules are
hydrogen bonds
Because of the Hydrogen bond weakness the
water molecules attract to any charged molecules
more than water molecules themselves

Water is powerful solvent for polar substances
Ionic compounds are polar substance such as
Sodium chloride ( NaCl )
Carbon containing molecule ( organic )with
ionised groups
( carboxyl –COO , Amino group –NH2)
Can be soluble in water ( glucose one of them)
Because it contains hydroxyl group –OH
Then glucose called solute and water called
solvent

3- Distinguish between
A-monosaccharides,
B-disaccharides
C-polysaccharides
(glycogen and starch )
( amylose and amylopectin)
relate their structures to their roles in providing and
storing energy
( ß-glucose and cellulose are not required in this topic).

Monosaccharide ( simple sugar )
1- they are the smallest molecule of carbohydrates
2-they are soluble in water and test sweet
3- glucose the most important monosaccharide
-All green leaves produce glucose in photosynthesis
- our bodies transport glucose in the blood
- all cells use glucose in respiration as energy source
-Glucose used as building block for many large molecule

Glucose structure
Molecular formula C6H12O6
We can write this formula on paper as linear but it
can not exist in linear form
Because each carbon arranges its four bonds
into TETRAHEDRON
So oxygen attaches carbon atom number
5 , 1

Other monosaccharide important in our cells
Fructose and galactose are example of hexose
Other monosaccharide important in our cells
Such as ribose / deoxyribose which are components of
NUCLIC ACIDS ( DNA / RNA )

4- Describe how monosaccharides join to form
disaccharides (sucrose, lactose and maltose)
and polysaccharides (glycogen and amylose)
through condensation reactions forming
glycosidic bonds, and how these
can be split through hydrolysis reactions.

Disaccharides
are carbohydrates made of 2 monosaccharides
Condensation is the chemical reaction name to
form disaccharide with glycosidic bond
Hydrolysis is the chemical reaction name to
add water molecule to break down the
glycosidic bond

Examples of disaccharides
Maltose made by condensation reaction of 2
glucose molecules
Lactose made by condensation reaction of
one galactose molecule and one glucose
molecule

Such as disaccharides , polysaccharides are made of
many MONOSACCHARIDE molecules linked together
by GLYCOSIDIC bond
Monomer changes into polymer
Starch and glycogen are poly saccharides and their
function is storing energy

Starch is a mixture of 2 poly saccharides
Amylose molecule is unbranched chain from
α glucose
Amylopectin molecule is branched chain

Glycogen is a polymer made of α glucose similar to
Amylopectin molecule is branched chain
Glycogen is found in liver cells and muscles fibers as
source of energy

Starch test

Describe the synthesis of a triglyceride by the
formation of ester bonds during condensation
reactions between glycerol and three fatty acids and
recognise differences between saturated and
unsaturated lipids.

Lipids can be found in animal as fats while it is
oils in plants
In room temperature
Fats are solid oils are liquids
Number of Oxygen atoms are less than in carbohydrates
Lipids are hydrophobic ( could not dissolve in water )
They are dissolved in organic solvents such as ALCOHOL

Fats and oils are compound called triglyceride
Triglyceride is formed by condensation reaction
Glycerol and fatty acid

Fats and oils are compound called triglyceride
Triglyceride classified as two types
Saturated ( fats ) with single bond in carbon chain
Unsaturated (oils ) with at least one double bond in
carbon chain which are called ( monounsaturated lipids)
while oils with more than one double bond are called
(Polyunsaturated lipids )

1 edexcel igcse human biology -cell and tissues

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