BIOLOGY ADVANCED LEVEL FULL NOTES
BIOLOGY ADVANCED LEVEL FULL NOTES: BIOLOGY FORM 5 cover seven (7)topics CYTOLOGY , PRINCIPLES OF CLASSIFICATION, NATURAL GROUPS OF ORGANISMS, COORDINATION NUTRITION, GASEOUS EXCHANGE AND RESPIRATION AND REGULATION (HOMEOSTATIS) & BIOLOGY FORM 6 Cover six (6) topics TRANSPORTATION ,GROWTH AND DEVELOPMENT , REPRODUCTION, GENETICS, EVOLUTION & ECOLOGY.
Cytology is the study of cellular structure, functioning, types, behavior, and framework and adaptations.
CYTOLOGY
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.
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STRUCTURE OF CELLS AND FUNCTIONS
The five structures are also known as ultra structure and are obtained by two techniques.
1. Physiological or metabolic activities take place within a cell. Viruses though are not cells, have life within their hosts.
2. 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.
3. 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.
4. Electronic microscope.
5. 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.
ANIMAL CELL STRUCTURES
Diagram of the animal cells under light and electron microscope.
DIAGRAM OF ANIMAL CELL UNDER ELECTRON MICROSCOPE
ANIMAL CELL STRUCTURES
Characteristics;
- Have irregular shape.
- Have centrioles.
- Have lysosomes.
- Lack cell walls.
- Lack plastids.
- Store carbohydrates in the form of glycogen e.g. phagocytotic vacuoles, pinocytotic vacuoles, autophagic vacuoles and etc.
- Cytokinesis occurs by furrowing i.e. periphery – centres direction of constriction of cell membrane.
STRUCTURE OF THE PLANT CELL
A plant cell is incased in a tough and rigid cellulose cell wall.
Beneath the cell wall is the cell surface membrane which surrounds the cytoplasm.
The latter contains organelles; the prominent being vacuole plastids e.g. chloroplasts and nucleus.
-Since a greater part of the cell is occupied by the vacuole, then the cytoplasm and nucleus are squeezed by the vacuole to the periphery.
-When viewed under light microscope; only a few structures are seen under high magnification power, even finer details are seen.
Diagram
Diagram of a plant cell under light microscope
CHARACTERISTICS OF PLANT CELLS
- It has a fixed shape.
- It has a cell wall made up of cellulose.
- It has large permanent vacuole,
- It has plastids; chloroplasts, chromoplast and leucoplasts.
- Stores carbohydrates in the form of starch.
- Lack lysosomes.
- Lack centrioles.
- Cell division; cytokinesis follows cento-periphery direction.
Similarities between a plant and an animal cell:
Both Have;
- Plasma membrane
- Distinct nucleus
- Ribosome
- Endoplasmic reticulum
- Cytoplasm
- Golgi apparatus
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