TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
THE CONCEPT OF CYTOLOGY.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
All chemical reactions/metabolic activities in the bodies of the organisms take place within the cells.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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.
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.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
The model suggests that the membrane is composed of proteins and lipids.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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Act as receptors for chemical stimuli.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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Allow the passage of fat soluble substances.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
These are involved in the selective transportation of polar molecules.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
It realizes the presence of phospholipids bilayer and protein layer.
The presence of polar head (hydrophilic) and non polar tail (hydrophobic) in the phospholipids.
It shows that the membrane is not static.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
It shows the presence of carbohydrates.
It shows that the protein layer is not continuous.
It indicates the presence of pores in the membrane passage of materials.
It protects the cytoplasm contents of the cells.
It allows passage of materials in and out of the cells since it has pores.
In some membranes e.g. those of the intestine cells, there are microvilli which increase the surface area for absorption of materials.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Acts as receptor sites for chemical stimuli such as hormones.
In nerve cells, the membrane is over lined with a fatty sheath (myelin sheath) which prevents the spreading of local currents to other neurons.
It aids cell to cell recognition when membranes of two cells come together.
The plasma membrane is a thin elastic membrane around the cell which usually allows the movement of small ions and molecules of various substances through it.
This nature of plasma membrane is termed as permeability.
The plasma membrane is permeable to water molecules.
To and fro movement of water molecules through the plasma membrane occurs due to the difference in concentration of the solutes on its either side.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
The process by which the water molecules pass through a membrane from region of higher water concentration to a region of lower water concentration is termed as osmosis.
The diffusion of a certain solute or substance takes place through the plasma membrane depends on the concentration and electrochemical gradient.
When molecules or ions move through the plasma membrane from low concentration to higher concentration, they require energy for such movement.
The energy is provided by ATP which is produced by the mitochondria.
Through the pores of plasma membrane some chemicals such as urea and glycerol could pass.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
It has been shown that large molecules of certain proteins also penetrate the cell.
The plasma membrane particles actively in the ingestion of certain large sized foreign or food substances.
The process by which the foreign substances are taken and digested is known as endocytosis.
In the process of exocytosis, the cells which have secretory functions such as pancreatic cells pass out their enzyme secretions outside the cell.
According to the nature of the food of foreign substance, endocytosis may be classified into two types;
It explains easily the known physical and chemical properties of the membrane.
It is the starting point to understanding the fix of the cell.
oAll membranes of the cell plus the tonoplast and those of the organelles have the fluid mosaic construction.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
NB: this point provides the clues about the distribution of cell membrane in the cell and its organelles.
NOTE:
This is the part of a cell, which is filled with fluid in the protoplasm.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
This part of the cell is the ground substance of the cell known as the hyaloplasm, where the cell organelles are suspended.
Cytosil is the soluble part of the cytoplasm.
Cytoplasm is distinguished into the following structures
Cytoplasm matrix
The space between plasma membrane and nucleus is followed by a morphous, translucent, homogenous liquid known as cytoplasm matrix and hyaloplasm.
The cytoplasm matrix consists of various inorganic compounds e.g.
carbohydrates, lipids, proteins, nucleon proteins, nucleic acids (RNA and DNA) and variety of enzymes.
The peripheral layer of a cytoplasm matrix is relatively non-glandular viscous and known as endoplasm.
Cytoplasm inclusion
The cytoplasm matrix contains many refractive granules of various sizes; these granules in the animal cells are known as cytoplasm inclusion.
The cytoplasm inclusion includes oil drops, yolk granules, pigments, secretory granules and glycogen granules.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Such granules in plant cells are known as plastids. The most common plastids are the chloroplasts (containing pigment chlorophyll), the leucoplastids (white color plastids) ,omyplastids ( the plastids that store starch) and lipoplastids ( which contain fats).
NB: plastids like cytoplasmic inclusion having only storage functions but also perform various important synthesis and metabolic activities such as the production of food materials due to the presence of chloroplasts.
Characteristics;
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Have irregular shape.
Have centrioles.
Have lysosomes.
Lack cell walls.
Lack plastids.
A plant cell is incased in a tough and rigid cellulose cell wall.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
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.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Lack lysosomes.
Lack centrioles.
Cell division; cytokinesis follows cento-periphery direction.
Plasma membrane
Distinct nucleus
Ribosome
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Endoplasmic reticulum
Cytoplasm
Golgi apparatus
An organelle is a distinct part of a cell which has a particular structure and function e.g. Mitochondria, chloroplast, ER etc.
CELL WALL
Cell wall is the structure that occurs externally to the cell.
Organisms with cell wall include.
Bacteria – have cell wall made up of murein and peptidoglycogen.
Fungi – has cell wall made up of chitin.
Algae and plant have cell wall made up of cellulose.
These are polysaccharides of galactose and galactronic acid.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Control cell growth and shape.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
The system of interconnected cell walls (apoplast) is a major pathway of the movement of water and dissolved mineral salts.
The cell walls are held together by middle lamellae, they also posses minute pores through which structures called plasmodesmata form living connections between cells and allows the protoplast to be linked in a system called symplast.
Reduction of water loss and reduced risk of infection (due to its waxy cuticle).
Transportation of materials. The walls of xylem vessels and sieve tubes are adopted for long transportation of materials through the cells.
Barrier to water movement.
The cell walls of root endodermal cells are impregnated with suberin that forms a barrier to water movement.
Some cell walls are modified as food reserves as in the storage hemicelluloses in some seeds.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Transport of materials by active transport.
The cell wall of transfer cells develops an increased surface area and this increases the efficiency and transfer materials by active transport.
CELL ORGANELLES OR ORGANOIDS.
It provides medium for chemical reaction to take place like protein synthesis, lipids synthesis and etc.
It stores useful materials such as amino acids, proteins, starch, carbohydrates, lipids, O2 etc.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
It stores waste materials such as C02 and nitrogen waste etc.
It controls the absorption of materials across the membrane due to its concentration gradient.
Is the cytoplasm matrix, is transverse by a vast reticulum or network at interconnecting tubules and vesicles which is known as endoplasmic reticulum or ER.
The endoplasmic is having a single vast and interconnected cavity which remains bounded by a single membrane.
The membrane of endoplasmic reticulum is supposed to be originated in pushings of plasma membrane
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
in the hyloplasm (matrix) because chemically it consists of a lipoproteinous structure like plasma membrane.
The membrane of the endoplasmic reticulum may be either smooth when they do not have attached ribosome and rough when they have the attached ribosome.
The membranes of endoplasmic reticulum are found to be continuous with the nuclear membrane and plasma membrane.
FUNCTIONS OF ENDOPLASMIC RETICULUM
Transport of materials from exterior to the nucleus or to cytoplasm organelles such as Golgi complex.
It provides mechanical support to the cytoplasm matrix.
Functions as a cytoplasm framework.
Surfaces for some of the biological activities of the cell catalyst its complex folding provide an enormous surface for such activities.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Synthesis and transfer of lipids.( smooth endoplasmic reticulum)
In the liver the smooth endoplasmic reticulum detoxifies many poisons and drugs.
The rough endoplasmic reticulum transports proteins synthesized in the ribosome of the rough endoplasmic reticulum.
Formation of Golgi bodies as they are modified endoplasmic reticulum.
Routes for movement of materials from the nucleus to the cytoplasm.
This cell organelle is also known as the Golgi body, Golgi complex or sityasome.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
It is the apparatus which consists of membranous sacs called cisternae and a system of small vesicle (called Golgi vesicles or dictysome vesicles) and vacuoles of various sizes.
The membranes of Golgi complex are of lipoproteins and these are supposed to be originated from the membrane of endoplasmic reticulum.
1. Produce secretions
There are many Golgi apparatus in;
Cells of salivary gland
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Cells of root cap
Cells of endocrine glands i.e. pancreas
Modification of materials.
The combination of carbohydrates and proteins to form glycoprotein takes place in them.
Many materials such as mucin are glycoprotein. It takes place in the cistern.
Carbohydrate chain + lipids = glycolipids
Production of carbohydrates example cellulose produced in plants after division. Thus this separates one cell from another.
Transport of lipids (storage and transport of proteins and lipids) after digestion, the fatty acids and glycerol are formed.
In the endoplasmic reticulum fatty acids and glycerol unite to form lipids (triglycerides).
The latter are passed to the Golgi apparatus where it transports them to the plasma membrane as lymphatic system and going to the lymphatic system.
Formation of lysosomes.
Synthesis of various types of carbohydrates from simple sugars.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
It activates the mitochondria to produce ATP.
It forms the acrosome of the sperms.
3. LYSOSOMES.
These are spherical single membrane bound organelles containing digestive enzymes.
-lipase
-carbohydrases
– Nucleases
The enzymes are synthesized in ribosome RER transported to the Golgi apparatus for modification.
The Golgi vesicles are detached from the Golgi apparatus and remain in the cytoplasm as lysosomes because they contain digestive enzymes.
FUNCTIONS
Play role in some developmental process e.g. remolding of bones and fractures.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
1. A vacuole is a fluid filled sac which is bound by a single membrane.
In animal cells, there are relatively small and temporary vacuoles such as phagocytotic, pinocytotic, autophagic vacuoles in plant cells; the vacuole is large and occupies a greater proportion of the cytoplasm.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
The membrane bounding the vacuole is the tonoplast and the fluid inside is the cell sap or vacuole sap.
The cell sap is a mixture of many substances; concentrates solutions of sugar, salt, organic acids, gases such as C02 and oxygen, pigments and waste products of metabolism.
It also contains enzymes similar to those of lysosomes.
They contain enzymes similar to those of lysosomes when plant cell dies.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Between the two membranes there is a space, the intermembranal space.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
The main function of mitochondrion is to yield energy during respiration.
About 98% of energy is synthesized e.g. one molecules of glucose yield 38 ATP.
Out of 38ATP 36 is synthesized in the mitochondrion by the reactions of Krebs cycle and electron transport chain.
Thus it is called power house or POWER station or power plant of the cell.
Adaptations of the mitochondrion to energy production
Presence of outer membrane and inner membrane to allow entry and exit of materials.
The inner membrane is coiled to increase the surface area for attachment of enzymes responsible for electron transfer.
Presence of matrix which is as granular and gives enough space for reaction to take place (Krebs cycle reaction) also matrix contains Krebs cycle enzymes.
Presence of circular DNA for replication of the mitochondrion.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Have 70s ribosome’s for synthesis of proteins.
Presence of phosphate for production of ATP.
Presence of Oxysome and water accompany aerobic respiration.
NB: The inner folded to form partitions called cristae which enables different types of metabolic activities to take place.
This phenomenon is called compartmentalization hence enables multienzymes systems to operate.
ENDOSYMBIOTIC THEORY
It is sensitive to different antibiotics such as chlorophyll and streptomycin which inhibit mitochondrial activities.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Chromoplasts
Leucoplasts
Chloroplasts
These are types of plastids bearing pigments i.e. yellow, red, orange, purple pigments.
Found in
Flowers
Fruits
Seeds
Leaves
Roots of carrots.
Leuco- colour / white.
These are colour plastids found mainly in storage organs. There are various types of leucoplasts;
Amyloplasts- contain starch
Lipoplasts – stores lipids
Proteoplasts- stores proteins
-Between the membranes there is the inter membrane space.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
It is the site of photosynthesis.
This is the process whereby green plants manufacture food from CO2 and water in the presence of light energy, it stores starch temporarily.
The thylakoids have chlorophyll pigment for trapping sunlight energy.
It has grana and thylakoids to hold the chlorophyll in proper position for maximum absorption of light energy.
Stroma contains enzymes for dark reactions of photosynthesis.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Presence of phosphate which acts as a source of phosphate during phosphorylation.
Ribosomes and circular DNA for synthesis of proteins such as enzymes
Endosymbiotic nature of chloroplasts and mitochondria.
The chloroplast and the mitochondria are endosymbiotic structures within a cell.
They are capable of leading life within a cell because;
They have double membrane which allows passage of materials in and out of their inside.
They have their own hereditary materials i.e. circular DNA.
They are capable of self replicating.
They have ribosomes (70’s) thus synthesize proteins. E.g. enzymes.
Have matrix or stroma, the ground substance where various reactions take place.
STROMA; various photosynthetic membrane are found where light reactions take place and dark reactions in the aqueous part.
MATRIX: Krebs cycle of respiration.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
They have their own enzyme system.
Therefore chloroplasts and mitochondria are said to be cells within cells.
The endosymbiotic nature of chloroplasts and mitochondria can be described as serial endosymbiotic theory (SET).
SERIAL ENDOSYMBIOTIC THEORY.
This theory accounts for the evolution of eukaryotic cells from prokaryotic cells.
Evidence / similarities of organelle and prokaryotic cells
Double membrane as cell membrane.
Circular DNA. 70’s ribosomes.
System of enzymes.
-It suggests that prokaryotic heterotropes ingested other mitochondrion like prokaryotic and roughly at the same time began forming an organized nucleus.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Chloroplasts, mitochondria and bacteria have features in common.
Enumerate the features to reveal the truth of this statement.
Where in the body would you expect to find large number of mitochondria? Give reasons.
If mitochondria were to perform the function of the function of the chloroplast, what modification would it require.
These enzymes catalyse the hydrolysis of hydrogen peroxide in water and oxygen.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
3.The leaf of peroxisomes are centers of photorespiration, especially in C3 plants
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-Each fibre is composed of two chains of protein loosely twisted about one another in helical manner.
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When the skin dies the intermediate filament of the cytoskeleton persists.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
They bring about movement of chromosomes during metaphase in nuclear division.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Since they are tubular, they transport materials from one part of the cytoplasm to another, i.e. they are cytoconductors.
In cilia and flagella, they help in rhythmical beating up movement.
They determine the shape of the cell. (Skeletal support).
The cilia and flagella are made up of proteins adenosine triphosphate (ATP).
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Each centriole is composed of nine paired thin threads and is in the form of cylinder.
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These are semisolid granules ground substance or matrix.
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Nucleolus
Chromatin
Matrix (aqueous)
Chromatin threads are grainy network of strands that undergo cooling into rod-like structures called chromatin.
Chemically chromatin and therefore chromosomes contains DNA (deoxyribose nucleic acids) and much protein and some RNA (ribonucleic acids) and few minerals.
These are small dark regions where different RNA type examples ribosomal RNA is produced and RNA joins the protein to form the subunit of ribosomes.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
-It synthesizes the ribosomes protein and is used in controlling the cell division.
Similarities between prokaryotic and eukaryotic cells.
Both have;
1. Structure for movement (cilia and flagella) 2. Cell wall.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
Cell membrane.
Ribosome’s.
Genetic material.(DNA) 6. Storage of food organelles.
QUESTIONS
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Give two functions of the cell membrane.
TOPIC 1: CYTOLOGY (I) ~ BIOLOGY FORM 5
This is the specialization of a cell in terms of both structure and functions.
Ability of a cell to perform single function is called cell specialization.
Cells work in interdependence with each other such that such that group of cells must be coordinated so that they carry out their activities efficiently such coordination is called integration.