Notes Biology O level final
Unit 1 Basic Organisms and Life Processes
Chapter 1 Cell Structure
Introduction to biology: To call an organism a "living organism," it must exhibit seven life processes:
Movement: Any change in position or direction.
Respiration: A chemical process inside the cell, breaking down food to release energy.
NB: Breathing is a physical process involving air entering and exiting the lungs.
Sensitivity: The ability to respond to changes in the surroundings.
Growth: Increase in cell number or size.
NB: Development is the increase in cell complexity (Cell → Tissue → Organ → Organ system → Living organism).
Reproduction: Producing offspring with the same basic characteristics as their parents.
Excretion: Getting rid of metabolic waste products (e.g., urea from kidneys, carbon dioxide from lungs, sweat through the skin).
NB: Egestion is getting rid of undigested food as feces through the anus.
Nutrition: Intake of food for energy and growth.
Cell Types
Cells are of two types:
Eukaryotic cells: Contain a nucleus; can be single-celled or multicellular (plants and animals).
Plant Cell:
Cell wall:
Non-living.
Fully permeable.
Made of cellulose.
Supports and protects the cell.
Maintains the cell's shape.
Cell membrane:
Living.
Selectively permeable.
Made of proteins, carbohydrates, and mainly fats.
Controls what enters and exits the cell.
Cytoplasm:
Jelly-like structure (70% water).
The living material that makes up the cell.
Site of all metabolic reactions.
Mitochondrion (Plural: Mitochondria):
Sausage shape.
Site of aerobic respiration to release energy.
Chloroplast:
Found in plant leaves' cells.
Contains chlorophyll pigment that traps sunlight for photosynthesis.
Large permanent sap vacuole:
Found in plant cells.
Supports and maintains the turgidity of the cell.
Nucleus:
Contains genetic information on DNA arranged in chromosomes.
Controls all metabolic reactions of the cell.
Controls cell division.
Ribosomes:
Site of protein synthesis.
Prokaryotic cells: Do not contain a nucleus; only single-celled organisms (Bacteria).
Specialized Cells
Root hair cells:
Function: Absorb water and mineral ions from the soil.
Adaptations:
Finger/hair-like projection increases the surface area for absorption.
Thin cell walls and membrane shorten the distance moved by water and mineral ions.
No chloroplasts, as no sunlight reaches the roots.
A very concentrated sap vacuole for more water absorption by osmosis.
A huge number of mitochondria for more absorption of mineral ions by active transport.
Red blood cells:
Function: Transport oxygen to all body parts.
Adaptations:
Biconcave shape increases the surface area for more oxygen diffusion.
Thin cell membrane shortens the diffusion distance.
Elastic cell membrane squeezes through narrow capillaries.
Contain Hemoglobin, the oxygen-carrying protein.
No nucleus or organelles provide more space for hemoglobin.
Smallest body cells to pass through narrow capillaries.
Sperm cells:
Function: Fuse with the female gamete, forming a zygote.
Adaptations:
Contain a haploid nucleus to restore the complete number of chromosomes after fertilization.
Huge number of mitochondria to release energy for swimming.
Mini size to consume less energy.
Many to increase the chance of fertilization.
Motile to be able to swim easily.
Ova cells:
Function: Fuse with the male gamete, forming a zygote.
Adaptations:
Contain a haploid nucleus to restore the complete number of chromosomes after fertilization.
Large to increase the chance of fertilization.
Contain a lot of food store for the growth and development of the fetus.
Have lots of cytoplasm to support the many divisions that they undergo.
Chapter 2 Movement of Substances Inside & Outside the Cell
Diffusion: Movement of molecules from a region of higher concentration to a region of lower concentration (down the concentration gradient). It is a passive process.
Factors affecting the rate of diffusion:
Temperature: Increasing temperature provides molecules with more kinetic energy, leading to a higher rate of diffusion.
Concentration gradient: The steeper the concentration gradient, the higher the rate of diffusion.
Thickness of the membrane: The thinner the membrane, the shorter the distance moved, leading to a higher rate of diffusion.
Surface area to volume ratio: The smaller the organism, the higher the surface area to volume ratio, leading to a higher rate of diffusion.
Osmosis: Movement of water from a region of higher water potential to a region of lower water potential through a partially permeable membrane (down the water potential gradient). It is a passive process.
NB: Factors affecting osmosis are the same as those affecting diffusion.
Osmosis is the diffusion of water through a partially permeable membrane.
Active transport: Movement of molecules from a region of lower concentration to a region of higher concentration (against the concentration gradient). It needs energy and carriers.
Factors affecting active transport:
Temperature
Number of carriers
Number of mitochondria
Chapter 3 Nutrition
Balanced diet: A diet containing the right proportions of all types of biological molecules to keep you healthy.
Biological molecules:
Carbohydrates:
Basic elements: Carbon, Hydrogen, and Oxygen, with a hydrogen: oxygen ratio of 2:1.
Building units: Monosaccharides (glucose, galactose, and fructose).
Complex forms: Disaccharides (maltose, lactose, and sucrose) and polysaccharides (starch, glycogen, and cellulose).
Properties: Monosaccharides and disaccharides are small, sweet, and soluble in water. Polysaccharides are large, non-sweet, and insoluble in water.
Functions:
Main source of energy (17 \, kj/g).
Glucose is the respiratory substrate.
Starch is the storage form of carbohydrates in plants.
Glycogen is the storage form of carbohydrates in animals.
Cellulose is used in the formation of cell walls in plants.
Lipids:
Basic elements: Carbon, Hydrogen, and Oxygen, with a hydrogen: oxygen ratio more than 2:1.
Building units: Fatty acids and glycerol.
Functions:
Highest source of energy (39 \, kj/g).
Formation of the cell membrane.
Act as a heat insulator under the skin.
Act as an electric insulator around the nerves.
Act as cushions around internal organs.
NB: Animal fats are solid at room temperature, while plant fats are liquid. Plant fats are healthier.
Proteins:
Basic elements: Carbon, Hydrogen, Oxygen, and Nitrogen (maybe sulfur)
Building units: Amino acids
Complex form: Polypeptides
Functions:
Source of energy (17 \, kj/g).
Formation of enzymes, hormones, hemoglobin, and antibodies.
Formation of muscles.
Minerals:
Calcium:
Importance: Formation of bones and teeth
Source: Milk and dairy products
Deficiency: Weak bones and teeth
Iron:
Importance: Formation of hemoglobin
Source: Red meat, liver, and spinach
Deficiency: Anemia
Vitamins:
Vitamin A:
Importance: Formation of rods in the retina
Source: Carrots and fish liver oils
Deficiency: Night blindness
Vitamin C:
Importance: Formation of healthy connective tissue and skin
Source: Citrus fruits and fresh vegetables
Deficiency: Scurvy
Vitamin D:
Importance: Absorption of calcium from the intestine and its deposition in bones
Source: Fish liver oils and eggs
Deficiency: Rickets in children and weak bones in adults
Fibers:
Importance:
Help in weight loss
Help in peristalsis, so prevent constipation
Decrease risk of colon cancer
Source: Lettuce & cereals
Water:
Constitutes about 70% of the human body
Importance:
Acts as a solvent of reactants
Transporter of all substances
NB: Sunlight activates vitamin D in the body.
Malnutrition: Eating either too much or too little of one or more types of biological molecules.
Too much feeding leads to obesity, hypertension, diabetes, and cardiovascular diseases.
Too little feeding leads to starvation.
NB: Undigested food is mainly cellulose, and humans do not have the cellulase enzyme.
Chapter 4 Enzymes
Enzymes: biological catalysts which speed up the rate of reaction without being used up or consumed.
Enzymes consist of an inactive body and an active site where the reaction takes place.
Substrate: the molecule that an enzyme acts on.
Enzymes work by lowering the activation energy.
The active site shape is complementary to the substrate shape, forming the key and lock model.
Enzymes are specific; each enzyme will only catalyze one reaction. That’s why cells contain hundreds of different enzymes.
Factors affecting enzyme activity:
Temperature:
Area A: Increasing temperature increases the rate of reaction.
Explanation: Increasing temperature increases kinetic energy, increases the frequency of successful collisions, so Larger numbers of enzyme-substrate complexes, leading to a higher rate of reaction.
Area B: Temperature 40^oC is the optimum temperature.
Explanation: Increasing temperature to 40^oC, highest kinetic energy, highest frequency of successful collisions, largest number of enzyme-substrate complexes, leading to the highest rate of reaction.
Area C: Increasing temperature above the optimum decreases the rate of reaction.
Explanation: Proteins are broken down by heat, so enzymes are denatured (permanent loss of the active site shape, and can no longer fit its substrate).
NB: At both extremes, the rate of reaction equals zero. At the lower extreme enzymes are deactivated (reversible), while at the higher extreme enzymes are denatured (Irreversible).
pH:
The highest rate of reaction takes place only at the optimum.
Small changes from the optimum decrease the rate of reaction.
Large changes from the optimum denature the enzymes.
NB: At both extremes, enzymes are denatured.
Enzyme concentration:
Area A: Increasing the enzyme concentration increases the rate of reaction.
Explanation: Increasing enzyme concentration increases the chance of successful collisions, so larger numbers of enzyme-substrate complexes, leading to a higher rate of reaction.
Area B: Increasing enzyme concentration has no effect on the rate of reaction.
Explanation: No more substrates are available.
Substrate concentration:
Same as enzyme concentration.
Chapter 5 Cellular Respiration
Aerobic respiration: Occurs in all animals, plants, and many other organisms' cells when the oxygen supply is higher than the oxygen demand.
Glucose + oxygen \rightarrow carbon \, dioxide + water + energy
C6H{12}O6 + 6O2 \rightarrow 6CO2 + 6H2O + 36ATP
NB: ATP is the energy currency of the cell.
Anaerobic respiration: Cells respire without using oxygen. Glucose is not completely broken down, so less energy is released.
Yeast Cells:
Used in commercial processes such as making beer and baking bread.
Occurs in the absence of oxygen.
Glucose \rightarrow Ethanol + carbon \, dioxide + Energy
Muscle Cells:
Occurs during exercise when the oxygen demand increases until it exceeds the oxygen supply.
Muscle cells respire anaerobically, releasing lactic acid that accumulates in the muscle, leading to severe pain (Muscle cramp).
When the person stops exercising, the oxygen demand decreases and the oxygen supply is still high, so the excess oxygen breaks down the lactic acid into carbon dioxide and water relieving the pain. This is known as ‘repaying oxygen debt’.
Glucose \rightarrow lactic \, acid + Energy
NB:
Energy budget: A relationship between energy input (intake of food) and energy output (exercise).
Energy requirements vary according to:
Level of activity:
High level of activity means more muscle contractions, so more aerobic respiration to release more energy.
Age:
The younger the age, the higher the level of activity, more muscle contractions, so more aerobic respiration to release more energy.
Pregnancy:
Needs more energy as:
She is carrying extra weight.
Energy needed for the growth and development of her fetus.
Chapter 6 The Variety of Living Organisms
Biologists classify the more than ten million species of organisms alive on Earth today into 5 kingdoms.
Kingdoms of living organisms:
Plant kingdom
Animal kingdom
Fungal kingdom
Protoctists kingdom
Bacterial kingdom
Types of nutrition:
Internal digestion:
As in animals and plants.
Done by ingestion of nutrients.
External digestion:
As in bacteria, fungi, and protoctists.
Done by secreting extracellular enzymes to breakdown the nutrients, then absorbing the Products by diffusion back to the cell.
Divided into three types:
Parasitic: Feeding on living cells causing diseases.
Saprotrophic: Feeding on dead cells (decomposition).
Symbiotic: Exchanging benefits (e.g., nitrogen-fixing bacteria which feed on the roots of Plants, but in return, it converts nitrogen gas into nitrates in the soil).
Bacterial Kingdom
All bacteria are unicellular, as they're Prokaryotic organisms.
Some types of bacteria have chlorophyll in the cytoplasm to undergo photosynthesis.
Some bacteria are parasitic (e.g., vibrio cholera, which causes cholera disease), some are saprotrophic, and some are symbiotic as nitrogen-fixing bacteria.
Some types of bacteria can respire aerobically, some can respire anaerobically, and some can respire both (facultative).
Bacteria reproduce asexually (by binary fission).
Fungal Kingdom
All fungi are multicellular, except yeast, which is unicellular.
Fungi store carbohydrates in the form of glycogen.
Some fungi are Parasitic (e.g., candida, which causes thrush), and some are saprotrophic.
Most fungi respire anaerobically.
Fungi reproduce asexually as budding in yeast.
Protoctist Kingdom
Mixed group of organisms that don’t fit into any kingdom.
Unicellular
Nucleated
Examples:
Amoeba (like animals).
Algae (is like plants).
Plasmodium malariae parasitic causing malaria.
Viruses
Not made of cells.
They don’t have nucleus or cytoplasm.
They are all Parasitic.
They don’t feed, respire, move, grow or excrete.
They can only reproduce inside the host cell.
HIV causes AIDs
Influenza causes common colds
Tobacco mosaic virus decolorizes the Plant leaves
Unit 2 Animal Physiology
Chapter 1 Respiratory System
The respiratory system is lined by the respiratory epithelium:
Consisting of Columnar Ciliated cells with goblet cells
Mucus:
Maintains epithelial moisture and traps dust and Pathogens moving through the airway.
Cilia:
Removes mucus.
Nose:
Lined by mucus to keep the air moist.
Contains cilia to filter the air.
Rich in blood capillaries which warm the air.
Pharynx:
A wide space for the oesophagus and the trachea.
Larynx:
The organ of voice which contains the vocal cords.
It is closed during swallowing by a piece of cartilage called the epiglottis.
Trachea:
A hollow muscular tube.
Surrounded by incomplete C-shaped cartilage rings to prevent its collapse.
Bronchi:
The branches of the trachea which enter the lungs.
Same structure as trachea.
Bronchioles:
Small branches of the bronchi which end at the alveoli.
Pleural membranes:
They make up a continuous envelope around the lungs.
Filled with a thin layer of liquid called pleural fluid which prevents friction with the moving ribs.
Alveoli:
Building unit of the lung.
Responsible for gas exchange.
It is the diffusion of oxygen from alveoli to the blood and diffusion of carbon dioxide from blood to the alveoli.
Adaptations of alveoli for gas exchange:
Large total surface area (60m^2) for more gas exchange.
Surrounded by a rich network of blood capillaries to maintain a steep concentration gradient.
Thin wall to shorten diffusion distance.
Lined by a moisture layer to prevent drying out of cells and for the dissolving of gases.
Ventilation: Movement of air in and out of the lungs requires a difference in air pressure.
During inhalation:
Diaphragm contracts and flattens.
Intercostal muscles contract, pulling the ribcage upwards and outwards.
This increases the volume and decreases the pressure in the lungs.
So, air enters the lungs from higher pressure outside to lower pressure inside.
During exhalation:
Diaphragm relaxes and domes.
Intercostal muscles relax, pulling the ribcage downwards and inwards.
This decreases the volume and increases the pressure in the lungs.
So, air exits the lungs from higher pressure inside to lower pressure outside.
NB: During normal breathing, the elasticity of the lungs and the weight of the ribs acting downwards are enough to cause exhalation.
Gas percentages in atmospheric air vs. exhaled air:
Nitrogen:
Atmospheric air: 78%
Exhaled air: 78%
Oxygen:
Atmospheric air: 21%
Exhaled air: 16%
Carbon dioxide:
Atmospheric air: 0.04%
Exhaled air: 4%
Water vapor:
Atmospheric air: Variable
Exhaled air: High
Temperature:
Atmospheric air: Variable
Exhaled air: High
Effect of exercise on the respiratory system:
Before the exercise:
Secretion of adrenaline hormone, which increases the depth of breathing.
During exercise:
The breathing rate increases, more oxygen is delivered to muscles, more aerobic respiration occurs to release more energy, so better muscle contractions.
After the exercise:
The breathing rate is still high, for the excess oxygen to breakdown the lactic acid that was formed during anaerobic respiration. This is known as repaying oxygen debt.
Hazards of Smoking:
Tobacco smoking is a major risk factor for heart and lung diseases.
Every year nearly 6 million people die from tobacco-related illnesses.
Main ingredients:
Nicotine:
A brain stimulant, so it is highly addictive.
Increases the heart rate and blood pressure, So, it increases the risk of cardiovascular diseases.
Carbon monoxide:
Binds with the hemoglobin forming carboxyhemoglobin which reduces oxygen delivered to all tissues.
Damages endothelium of blood vessels which stimulates deposition of cholesterol blocking arteries.
Tar:
Highly carcinogenic.
Increases secretion of mucus and damages cilia.
Accumulation of mucus attracts bacteria causing bronchitis.
Mucus is removed by coughing.
Repeated coughing ruptures the alveoli which reduces the surface area for gas exchange (Emphysema).
Chapter 2 Digestive System
Food contains carbohydrates, lipids, and proteins, but they're not the same carbohydrates, lipids, and proteins as in our tissues.
Food passes through different processes in our gut:
Ingestion: Intake of food through the mouth.
Mechanical digestion: Breakdown of large food pieces into small ones.
Chemical digestion: Breakdown of large insoluble food molecules into smaller soluble ones by enzymes.
Absorption: Transfer of digested food from the intestine to the blood.
Assimilation: Making use of soluble absorbed food molecules.
Egestion: Getting rid of undigested food in the form of feces through the anus.
Mouth:
Mechanical digestion:
Chewing action by the teeth to increase the surface area of food for better enzyme activity.
Chemical digestion:
Salivary glands secrete the salivary juice which contains:
Salivary amylase which breaks down starch into maltose.
Sodium bicarbonate provides the optimum pH for the salivary amylase activity.
Water and mucus for moistening the food.
Oesophagus:
Mechanical digestion only.
Peristalsis: Waves of contractions and relaxations of the circular and longitudinal muscles in the esophagus wall, pushing food downwards.
Stomach:
Mechanical digestion:
Churning action to mix the food with the gastric juice.
Chemical digestion:
Stomach secretes the gastric juice, which contains:
Pepsin enzyme which breaks down proteins into polypeptides.
Hydrochloric acid (HCl) which:
Provides optimum pH for pepsin activity.
Activates pepsinogen into pepsin.
Kills bacteria, helping to protect us from food poisoning.
Small Intestine:
The first part is the duodenum, where digestion is completed. It also receives bile juice from the liver and the pancreatic juice from the pancreas to aid in digestion.
Bile juice contains:
Sodium bicarbonate neutralizes the acidity of food coming from the stomach.
Bile salts break down large fat globules into smaller ones (emulsification of fats) to increase their surface area. "Mechanical digestion"
Bile pigments are waste products from breaking down RBCs in the liver (no role in digestion).
NB: Bile juice is stored in the gall bladder.
Pancreatic juice contains:
Sodium bicarbonate neutralizes the acidity of food coming from the stomach.
Pancreatic amylase breaks down starch into maltose.
Trypsin breaks down polypeptides into amino acids.
Lipase breaks down lipids into fatty acids and glycerol.
*Intestinal juice Contains:
Maltase which breaks down maltose into glucose.
Lactase which breaks down lactose into glucose and galactose.
Sucrase which breaks down Sucrose into glucose and fructose.
Ileum: Site of absorption Adaptaions:
Very long (Up to 6 meters) to increase the surface area for complete absorption of food.
Contains villi covered by microvilli to increase the surface area for absorption of food.
Villi contain a rich network of blood capillaries to maintain a steep concentration gradient and for the absorption of food except lipids.
Villi contain lacteals for the absorption of lipids.
Villi have thin walls (one cell thick) to shorten diffusion distance for food.
Large Intestine:
Site of feces formation, by absorbing water from undigested food.
NB Over absorption of water hard stony feces (constipation)
NB Under absorption of water watery feces (Diarrhea)
Rectum:
Stores feces
Anus:
Expels feces
Chapter 3 Circulatory system
Blood is pumped around a closed circle made up of the heart and blood vessels, as it travels around the body.
There are two main types of circulatory systems in animals:
Single circulation:
The blood is pumped from the heart to the gas exchange organ and then directly to the rest of the body.
(As in fish).
Double circulation:
The blood is pumped from the heart to the gas exchange organ, back to the heart, and then to the rest of the body.
(As in humans).
Heart
*Heart Structure
*The heart consists of:
* 4 chambers
* 2 atria
* Left atrium
* Right atrium
* 2 ventricles
* Left ventricle
* Right ventricle4 valves
* 2 atrioventricular valves
* Bicuspid valve on left side
* Tricuspid valve on right side
* 2 Semilunar valves
* Aortic semilunar valve on left side
* Pulmonary semilunar valve on right side
NB The function of the valve is to allow blood flow in one direction and prevent back flow in the opposite direction4 major blood vessels
* Pulmonary vein entering left atrium
* Aorta exiting left ventricle
* Vena cava entering right atrium
* Pulmonary artery exiting right ventricleSeptum
* Separates the right side from the left side, so prevent mixing the oxygenated blood from the deoxygenated blood
Double circulation means that blood passes by the heart twice per cycle
Circulation through the heart:
Pulmonary circulation:
Deoxygenated blood leaves the heart through the pulmonary arteries, and is circulated through the lungs, where oxygen is added, and carbon dioxide is removed. The oxygenated blood returns to the heart through the pulmonary veins.
Systemic circulation:
Oxygenated blood leaves the heart through the aorta and is circulated through all other parts of the body, where it unloads its oxygen. Deoxygenated blood returns to the heart through the vena cava.
A double circulation is more efficient than a single circulation as high pressure is maintained and blood travels more quickly to organs
Cardiac Cycle:
Atrial systole: both atria contract to pass blood to the ventricles and both AV values are open.
Ventricular systole: both ventricles contract to pass blood to the major arteries (Aorta and the pulmonary arteries) while the AV valves are closed to prevent backflow of blood and semilunar valves are open.
o The left ventricle is the chamber with the thickest wall and the aorta is the vessel with the highest pressure.
o The highest oxygen concentration is in the pulmonary vein.
o The highest carbon dioxide concentration is in the pulmonary artery.
o The blood supply of the heart is the coronary arteries which are direct branches from the aorta.
Diastole: Relaxation of all heart chambers (cardiac filling).
*
Cardiac Cycle
Effect of exercise on the heart:-
During exercise, there is more adrenaline released in the body, which increases heart rate and stroke volume leading to higher cardiac output more oxygenated blood reaches muscles more aerobic respiration more energy released better muscle contractions less anaerobic respiration less lactic acid less muscle fatigue.
Heart rate: number of beats in one minute.
Stroke volume: Volume of blood pumped by the heart in one beat.
Cardiac output: Volume of blood pumped by the heart in one minute.
BMI takes both weight and height into consideration, so it allows for a more valid comparison than just measuring body mass.
Body Mass Index (BMI):
Obesity is an increasing problem in the world. You can calculate whether you are obese or not by calculating your BMI.
BMI = \frac{Body \, mass \, in \, kg}{(Height \, in \, m)^2}
Benefits of regular exercise: Strengthens the cardiac muscle so it has more forceful contractions. This increases stroke volume leading to a higher cardiac output.
Coronary heart diseases (CHD):
The coronary arteries are among the narrowest in the body. They are easily blocked or damaged.
Injury of the endothelium lining due to many factors as smoking and hypertension.
This leads to accumulation of cholesterol, blocking the lumen of the coronary artery.
This blockage reduces oxygen supply to the cardiac muscles which stops aerobic respiration.
Anaerobic respiration occurs which produces lactic acid.
Lactic acid lowers PH which denatures the enzymes.
Leading to death of the part supplied by the blocked artery (Myocardial infarction).
*Risk factors of CHD:
Smoking: As nicotine increases blood pressure and carbon monoxide damages the endothelium.
High blood pressure puts more load on the heart.
Diet: Eating large amounts of animal fats.
Stress: Raises blood pressure.
Lack of exercise: Regular exercise helps to reduce blood pressure and strengthens the heart.
The Blood Vessels
Direction of blood flow
Arteries Exiting the heart
Capillaries Connecting arteries to veins
Veins Entering the heart
Function Carry oxygenated blood except the pulmonary artery carries deoxygenated blood
Deliver oxygen and nutrients.
Collect carbon dioxide and waste products
Carry deoxygenated blood except pulmonary vein carries oxygenated blood
Wall Thick wall to withstand high pressure (rich in elastic fibers and smooth muscles)
Very thin wall (one cell thick) to shorten diffusion distance
The wall has pores to facilitate the exchange of substances
Thin wall (fewer elastic fibers and smooth muscles)
Lumen Narrow
Very small
Wide
Valves No, except pulmonary artery and aorta
No
Yes
Pressure Highest
Lower than arteries & higher than veins
Lowest
Pulsation Yes
No
No
*Factors that ensure blood flow in veins:
Muscles around the veins pump to provide movement of blood back to the heart.
Valves in veins to prevent the back flow of blood.
Blood
Blood is a lot more than just a red liquid flowing through your arteries and veins. In fact, blood is a complex tissue.
Blood Plasma Cells
Dissolved Substances
Water 90%
RBCs Immune System
WBCs platelets
RBCs
Platelets
*Immune System
There are two main types which are:
Phagocytes: (about 70% of WBCs) "First line of defense"
They produce extensions in their cytoplasm surrounding the microorganism. Then engulf it and enclose it in a vacuole.
Once it is inside, the phagocyte secretes digestive enzymes into the vacuole to break the microorganism down and absorb its products by diffusion.
This is known as phagocytosis
Lymphocytes: (about 25% of WBCs) "Second line of defense"
They secret antibodies, complementary to the antigen of the pathogen. Forming antigen antibody complex for easy phagocytosis
Some lymphocytes do not get involved in killing microorganisms straight away. Instead, they develop into memory cells. These cells remain in the blood for a lifetime. They store information about any pathogen, so if the same pathogen re-infects a person, they produce larger number of antibodies in a shorter period
Blood clotting
Platelets are not whole cells, but fragments of large cells. They are responsible for blood clotting
Platelets produce thromboplastin that activates prothrombin into thrombin
Thrombin is an active enzyme that converts soluble fibrinogen into insoluble fibrin
Fibrin forms a mesh that traps blood cells forming blood clots.
Vaccination: giving the person the pathogen in the form of weakened or dead to stimulate formation of memory cells for a secondary immune response, to secrete large number of antibodies in a short period.
NB
Chapter 4 Excretory system
Macroscopic structure
Each kidney is supplied with blood through a short renal artery. Inside the kidneys, blood is filtered and then it passes out through the renal vein.
Microscopic Structure
Nephron is the building unit of the kidney. There are about a million of these in each kidney.
The glomerulus has higher pressure than other capillaries as:
It has narrower capillary pores.
The vessel entering it is wider than the vessel leaving it
Formation of urine This occurs through 2 Phases:
Ultra filtration:
Separation of very small molecules from larger ones under high pressure of the glomerulus
This occurs at the Bowman’s capsule membrane
All blood components are filtered except blood cells and plasma proteins (As they're too large to pass)
This occurs passively
Selective reabsorption:
The reabsorption of useful substances back to the blood by active transport
This occurs along the renal tubules.
All glucose is reabsorbed at the proximal convoluted tubules
Most of the water is reabsorbed at the collecting duct
Also, some salts and amino acids are reabsorbed back to the blood
This occurs by active transport
Functions of the kidney:-
Excretion Getting rid of metabolic waste products(urea
Osmoregulation Balancing of water and salts levels in the blood
The kidneys reabsorb the maximum possible concentration of glucose in the blood of a normal person. In diabetics, the kidneys may not be able to reabsorb all glucose. So, some glucose may be detected in the urine, due to the lack of insulin
The least concentration of urea is in the renal vein, Also the most balanced water and salts levels in the body
Kidney failure
It is a very common problem. It can be treated by kidney transplantation or dialysis
Kidney transplantation:
The transplanted kidney is placed in the pelvis to:
Be closer to the urinary bladder
Reduce surgical complications
Advantages of kidney transplantation:-
Permanent solution
No waste of time
No risk of infection
Disadvantages of kidney transplantation:-
Shortage of donors
Risk of surgical complications
Risk of Immunosuppressive drugs
Risk of tissue rejection
Tissue rejection
When an organ is transplanted into a person, lymphocytes recognize the foreign antigens and produce antibodies destroying them
To overcome tissue rejection:
The donor must have similar antigens to those of the recipient
The recipient takes Immunosuppressive drugs
Dialysis
Blood flows from a vein in