BIOLOGY NOTES ADVANCED LEVEL (FORM 5)

BIOLOGY NOTES ADVANCED LEVEL (FORM 5) cover seven (7) topics CYTOLOGY , PRINCIPLES OF CLASSIFICATION, NATURAL GROUPS OF ORGANISMS, COORDINATION NUTRITION, GASEOUS EXCHANGE AND RESPIRATION AND REGULATION (HOMEOSTA TIS)

CYTOLOGY

THE CONCEPT OF CYTOLOGY.

Cytology is the study of cellular structure, functioning, types, behavior, and framework and adaptations.

The study of biological cells is known as cytology. Because all living entities are made up of the basic life-forming unit known as a “cell,” cytology/cell studies is gaining popularity, regardless of whether the system is plant or fungal, animal, bacterial, or viral. A person who studies cell biology is known as a cytologist. Cytologists are also known as cell biologists since cytology has been referred to as “cell biology” for a long time.

THE CELL THEORY

The bodies of all living things are made up of cells.

Robert Hooke (1665) was the first person to discover a cell from a plant cork. The cells looked like boxes. Other people who studied the structure of cells are Lamark (1809), Detrochet (1824) and Turpin (1826).

Schleiden (1838) studied the plant cells and emphasized that the cells are organisms and entire animals and plants are aggregations of these organisms arranged according to the definite laws.

In 1839 Schwann, a German botanist stated that ” we have seen that all organisms are composed of essentially like parts namely of cells”.

IMPORTANCE OF CYTOLOGY

Cytology has been very important discipline in the research diagnosis and treatment of human diseases. Most of health problems people encounter involve the cell disturbances.

The study examines cell interaction. Studying how cells interact or relate to other cells or environments the cytologists can predict problems or examine the dangers to the cell and identity type of infections.

THE MAIN IDEAS OF THE CELL THEORY

1. All organisms are made up of cells.

2. The new cells are derived from the pre-existing cells by the process of cell division (mitotic and meiotic division).

3. All chemical reactions/metabolic activities in the bodies of the organisms take place within the cells.

4. The cells contain hereditary materials which are passed from one generation to another.

5. Given a suitable condition, a cell is capable of independent existence.

TOPIC 1:

CYTOLOGY , CYTOLOGY 2

TOPIC 2:

PRINCIPLES OF CLASSIFICATION

TOPIC 3:

NATURAL GROUPS OF ORGANISMS

TOPIC 4:

COORDINATION

TOPIC 5:

NUTRITION

TOPIC 6:

GASEOUS EXCHANGE AND RESPIRATION

TOPIC 7:

REGULATION (HOMEOSTA TIS)

CHALLENGES OF THE CELL THEORY

Hereditary materials are also found in viruses, mitochondria and chloroplasts, all of which are not viruses.

STRUCTURE OF CELLS AND FUNCTIONS

The five structures are also known as ultra structure and are obtained by two techniques.

Physiological or metabolic activities take place within a cell. Viruses though are not cells, have life within their hosts.
The new cells arise from pre-existing cells by cell division. In this postulate the theory does not specify about the origin of the first cell.
All living things must have cells. This postulate is challenged by the existence of viruses, where when they are inside the body of their host, viruses act as living things even though they don’t have cellular organization.
Electronic microscope.
Cell fractionation.

A cell is usually a tiny, three dimensional sac of many organelles which are suspended within an aqueous medium (the cytoplasm) containing or contained (bounded) by a cell membrane.

In the case of plants, a cell wall is bounded by a cellulose cell wall.

The bulk of these structures (organelles) of the cells is referred to as a cytoplasm.

Cytocil is the fluid part of the cytoplasm.

PROKARYOTIC CELLS.

They are extremely small for example bacteria all range from 0.5 – 10 micrometers.

They appeared about 350 million years ago.

Cells of prokaryotes lack the true nuclei that are their genetic material (DNA) are not enclosed by the nuclear membrane and lies freely in the cytoplasm.

EUKARYOTIC CELLS

The cells of eukaryotic have three basic parts

1. The plasma membrane.

2. The cytoplasm.

3. The nucleus.

Plasma membrane.

This is also called the cell surface membrane as plasma membrane or plasma lemma which separates the contents of the cells from the external environment, controlling the exchange of materials.

In animal cells it is an outermost layer where as in plant cells it is beneath the cell wall. E.g. neurillema in neurons.

Muscle cells – sacrolemma.

STRUCTURE OF THE CELL MEMBRANE

There are two models suggested by different scientist to try to describe the cell membranes.

These are;

i. Daniel-Davson model (1935)

ii. Fluid mosaic model (1972)

Daniel-Davson model

Diagram

According to Daniel and Davson, the membrane is structurally composed of two chemical substances that form their own layer.

1. Protein layer made up of molecules. The layer is continuous and lacks pores.

2. Phospholipids (at least two layers of phospholipids) oriented with their polar (hydrophilic ends near the surface and their non polar (hydrophobic) hydrocarbon chains in the interior of the membrane as far as possible from the

surrounding water.

According to the model, the membrane is structurally rigid static and non dynamic.

Strength of the model.

1. The model suggests that the membrane is composed of proteins and lipids.

2. Ampliphetic (double) nature of phospholipids such as phospholipids molecule has a polar head (hydrophilic) and a non polar tail (hydrophobic).

WEAKNESS OF THE MODEL

1. The model suggests that the protein layer is continuous. Researches done by scientists show that the protein layer is in-continuous.

2. The membrane is static is a wrong concept since the membrane is a dynamic ever changing structure.

3. Lack of pores in protein layers.

The protein molecules in a membrane have pores for passage of materials.

4. The model does not indicate the presence of a carbohydrate.

THE FLUID MOSAIC MODEL.

The model was put forward by singer and Nicolson 1972 in order to modify the Daniel and Davson model.

According to the fluid mosaic model, the membrane is an ever-changing structure in which the mosaic protein floats on the lipid bilayer acting as a fluid.

Proteins in this model do not form a continuous layer covering both sides of the membrane as proposed by Daniel and Davson model.

According to this model, the membrane has 3 constituents.

Lipids (45%)
Proteins (45%)
Carbohydrates (10%)

1. LIPIDS.

There are two types of lipids.

a. Glycolipids;

These are lipids associated with short carbohydrates chain.

ROLES OF GLYCOLIPIDS

Cell to cell recognition.

Act as receptors for chemical stimuli.

b. Phospholipids;

These are lipids associated with phosphates. They form 2 layers i.e. phospholipids bilayer. Each phospholipid consists of a polar head (hydrophilic) and a non polar tail (hydrophobic).
Act as a fluid and move about rapidly in their own layer. Since phospholipids are constantly in motion, the membrane is described as being fluidly.

ROLES OF PHOSPHOLIPIDS

1. Form the basic structure of the membrane.

2. Determine the fluidity of the membrane.

3. Allow the passage of fat soluble substances.

NB: cholesterol is a type of steroid located in between phospholipids keeping them fluidly.

ROLES OF CHOLESTEROL

1. Disturb the close package of phospholipids keeping them fluids.

2. Increase the flexibility of the membranes by allowing relative movements of the bilayers without actual displacement because it acts as an unsaturated fatty acid lubricating bilayer.

2. PROTEINS

These exist as globular in the membrane, i.e. they never form a continuous layer.

Within protein molecules or between adjacent there are poles. These may either be hydrophobic or hydrophilic.

Since the phospholipids are always in constant motion (fluid) proteins float in it forming a fluid mosaic model. The proteins are organized in a particular pattern known as mosaic.

There are protein molecules that extend/ transverse both layers of membranes. Other proteins are partially embedded in the membrane. These are called intrinsic proteins.

Some proteins float freely inside the membrane, hence they are called peripheral or extrinsic proteins.

TYPES AND ROLES OF PROTEINS.

1. Carrier proteins or channel proteins.

These are involved in the selective transportation of polar molecules. i.e. ions across the membrane

e.g. movement of glucose to the cell, chlorine ions. (Cl-)

2. Enzymes

Catalyze different metabolic reactions.

3. Receptor molecule.

Some act as receptors for chemical stimuli example hormones.

4. Antigen.

Identity markers. These are glycoprotein. They have different shapes in every kind of a cell. They have specific side chains thus are recognized by other cells and behave in an organized manner.

5. Energy transfer.

In some physiological processes such as photosynthesis and respiration, some proteins are involved in energy transfer (special form of membrane found in chloroplasts and mitochondria).

3. CARBOHYDRATES

These branches to the outside of the membrane as an antennae or feelers.

There are two types;

Glycoprotein ( carbohydrate chain – plus protein)
Glycolipids ( carbohydrate chain plus lipid)

BIOCHEMISTRY

ORGANIC CONSTITUENT OF THE CELLS.

Bio chemistry: is the study of structures, properties and functions of chemical constituents of the cells.

-It is a great unifying theme in biology.

It finds applications in fields like;

Agriculture; in developing pesticides and herbicides.
Medicine; including all pharmaceuticals.
Fermentation; baking products, food products and breweries.
New development of biology eg genetic engineering.

ELEMENTS FOUND IN LIVING ORGANISMS ARE

Chief/ macro elements: hydrogen (H), carbon(C), nitrogen (N), oxygen (O), phosphorous (P), sulphur(S).
Ions – sodium(Na⁺) , magnesium (Mg²⁺) , chlorine( cl^–) , calcium (Ca²⁺) etc.
Trace elements – manganese(Mn) , iron(Fe) , cobalt(Co),copper (Cu) , molybdenum(Mo) and iodine(I).

MACROMOLECULE(S)

Macromolecule is a giant molecule made from many repeating units. The molecules built are polymers and the individual units are monomers.

-The units are joined together by a chemical process called CONDENSATION which means removal of water.

-The units can be broken down again by an opposite process known as hydrolysis which means adding of water.

The most important macromolecules in biology are;

Polysaccharides( carbohydrates)
Protein
Lipids
Nucleic acids.

And their constituent monomers are; monosaccharide’s, amino acids, glycerol, fatty acids and nucleotides respectively.

Others are;

Adenosine triphosphate (ATP).

ORGANIC SUBSTANCES ( CHEMICAL NATURE AND IMPORTANCE)

1. CARBOHYDRATES

They are substances which contain carbon, hydrogen and oxygen with the general formula of (CHO)_n where n is a real number.

Characteristics of carbohydrates.

They are either simple sugars or compound sugars.

The compound sugars are formed by condensation of simple `sugar molecules.

They are hydrate of carbon from the proportion of hydrogen and oxygen in water.
The basic carbohydrate unit is thus a sugar which is the derivative of a poly hydrosol alcohol.

Alcohol is the paraffin compound with hydrogen atom replaced by the univalent hydroxyl (OH) group.
Paraffin is aliphatic or chain of compounds of carbon and hydrogen in which the carbon atoms are linked by single bonds to adjacent atoms. (see Example above).
The simpler hydroxyls are the glycol and glycerol and the simplest of sugar is the glycerose (glycerin).

The carbohydrate contains several hydroxyl groups.

4. Some contain aldehyde (-CHO) group and others contain ketone group ( -CO-)

Examples;

Glucose: is a pentahydroxyl alcohol with the aldehyde group.

GLUCOSE

BIOLOGY NOTES ADVANCED LEVEL (FORM 5) - ALL TOPICS

2. Fructose: is the pent hydroxyl alcohol with ketone group.

Complex sugars are built from the basic sugar units called monosaccharides through the process of condensation polymerization.

Many sugars are reducing sugars and others are non-reducing sugars but give rise to reducing sugars on hydrolysis with enzymes or mineral acid (mostly dilute HCL)

NB:Carbohydrates are called reducing sugar because they act as reducing agents supplying electrons from their functional groups i.e. the aldehyde and ketone groups which can reduce the cu²⁺ ions to cu⁺ ions which appear orange or yellow ppt (precipitate).

The true carbohydrates are saccharides with a combination of sugar units. These are divided into three main classes

monosaccharides – with a single sugar unit
Disaccharides – with two sugar units.
Polysaccharides- with many sugar units.

SUGAR

Sugar which include mono and disaccharides are all soluble in water. They have a sweet taste.

They are crystalline and small molecules.

Those with a potentially active aldehyde or ketone group are the reducing sugars e.g. glucose.

sugar	Natural occurrence
Glucose	Plant juice and grape sugar
Galactose	From fruits.
Fructose	From fruits
Maltose	From germinating seeds ( cereals)
Sacrose	From sugar cane ( in plants)
Lactose	From milk

Sugars without potentially active reducing groups are known as non-reducing sugars e.g.
Sucrose (C₁₂H₂₂O₁₁).

Monosaccharides

Have general formula (CnH2nOn)
All are reducing sugars
They are classified according to the number of carbon atoms e.g.;

Trioses have 3 carbon atoms

Tetraoses have 4 carbon atoms

Pentoses have 5 carbon atoms

Hexoses have 6 carbon atoms

Heptoses have 7 carbon atoms

-Of code, hexoses and pentoses are most common and triose being the true sugar.

-Pentose sugars are never occurring but only in combination with other groups

Of compounds.

Riboses- this occurs in one kind of nucleic acid. A derivative of deoxyribose

Hexose. The most important free sugar.

D-glucose

D- Fructose these are the most common sugars.

Structure of Monosaccharides

Glucose in common with other hexoses and pentoses easily forms stable ring structure. At any one time most molecules oxists as rings rather than
In case of glucose carbon atom number 1 may combine with the oxygen atom an carbon 5. This form a six -sided structure known as a pyranose ring
In case of fructose, carbon atom number 2 links with the oxygen an carbon atom number. This form a five sided structure known as furanose ring Both glucose and fructose can exist in beth
pyranose ring.

In case of fructose, carbon atom number 2 links with the oxygen on number 5. This form a five sides structure known as furanose ring Both glucose and fructose can exist in both pyranose and furanose
and furanose ring form.