1
Q
Metabolism
A
Refers to the chemical activities that occur within cells
2
Q
Structural levels of organisation
A
organism, systems, organs, tissues, cells, organelles & molecules
3
Q
Living things are composed of two major kinds of molecules:
A
- Inorganic molecules- do not contain carbon arranged in complex arrangements e.g. water and carbon dioxide.
- Organic molecules- do contain carbon arranged in complex arrangements e.g. polymers such as carbohydrates, proteins, lipids.
4
Q
Carbohydrates
A
Elements present: C, H, O
Monosaccharides (1 simple sugar unit): Glucose, Fructose, Galactose
Disaccharides (2 sugar units): Maltose, Lactose, Sucrose
Polysaccharides (many sugar units): Starches, Fibres, Glycogen
Functions in the body: mono- broken down to provide energy, di- energy, poly- energy storage and cellulose structure
5
Q
Lipids
A
The major groups include: Fats, oils, phospholipids and steroids.
Phospholipid:
elements present- C,H,O,P
components: 1x three-carbon glycerol backbone, 2x fatty acid molecules, 1x phosphate
function: make up the cell membrane
Triglyceride:
elements present- C,H,O
components: 1x glycerol, 3x fatty acids
specific examples: saturated, unsaturated, polyunsaturated
function: insulation, protect organs, energy source
6
Q
Proteins
A
They are made of amino acid units joined together to form polypeptide chains that are then twisted and combined to form protein molecules.
elements present: C,H,O,N,S
components: 20 amino acids
specific examples: Insulin, Amylase, Haemoglobin
function: catalysts, transport, support, receptors
7
Q
Nucleic Acids
A
elements present: C,H,O,N,P
RNA:
component- nucleotide (1 phosphate, 1 ribose sugar, 1 base (A,U,G,C))
examples: RNA, tRNA, mRNA, rRNA
function: directs protein synthesis, Hereditary materials (genes)
DNA:
component- nucleotide (1 phosphate, 1 deoxyribose sugar, 1 base (A,T,C,G))
examples: DNA
function: genetic code; codes for proteins
8
Q
Enzymes
A
A special group of proteins that act as biological catalysts that speed up chemical reactions by providing an alternate reaction pathway that has a lower activation energy for a reaction to proceed
- can be reused (don’t become part of the product)
- have a special shaped region called an active site that fits with the substrate.
- are very specific (act on one type of substrate only)
- names often end in ’ase’ eg. amylase, protease, lipase.
9
Q
Two major types of enzyme catalysed reactions
A
Catabolic Reactions- where enzymes speed up the break down of large molecules into two or more smaller molecules. eg. Digestion, Respiration
Anabolic Reactions- where enzymes speed up the making of large molecules from two or more smaller molecules. eg. Protein Synthesis, Photosynthesis
10
Q
Two enzyme actions models
A
Lock and Key Model - where the shape of the active site of enzyme (key) exactly fits the substrate (lock). NOTE: After the enzyme- substrate complex is formed (the key is turned), the reaction proceeds to produce new products and the enzyme is left over and available for repeat.
Induced Fit Model - where the shape of the active site of the enzyme changes slightly (active site moulds around substrate). NOTE: more widely accepted.
11
Q
Factors affecting enzyme action
A
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
- Cofactors…(eg. Large coenzymes or inorganic ions eg. Ca ions) enhance enzyme action by changing the shape of the enzyme & active site
- Inhibitors (eg pesticides –DDT & heavy metals – As, Pb, Cd)…decrease enzyme action by blocking active site or changing shape of this site
Note: pH, temperature, cofactors and inhibitors (all influence shape of the active site) and different enzymes have different optimum pH and temperature values.
12
Q
Denaturing by enzymes
A
Denatured enzyme- active site shape no longer fits with substrate
due to many factors e.g. temperature
13
Q
Cell membrane
A
- surround all cells (eukaryotic cells also have internal membranes)
- they are selectively permeable (allow some substances to cross them depending on their size, concentration, charge etc.):
allow oxygen, sugars, amino acids etc. into cells
allow carbon dioxide and wastes out of cells - are described by using the fluid-mosaic model. ie. There are many different types of molecules in and attached to membranes (mosaic) & these molecules can move sideways and across membrane (fluid) .
14
Q
The major groups of molecules found in / attached to membranes are:
A
Phospholipids- These molecules make up the ‘matrix’ of the membrane and are arranged to form two layers (in a bilayer). They separate the internal from the external cellular environments.
Proteins- embedded in the phospholipid bilayer and attached to the membrane outer-surface. Proteins function as: receptor sites (for hormones), transport facilitators, enzymes, antigens, binding sites).
Cholesterol- wedged between phospholipid molecules in eukaryotic cells. Function to increase flexibility at cooler temperatures
Carbohydrates- maybe attached to proteins or phospholipids- aid in cell recognition
15
Q
Two types of transport across membranes
A
Passive (no energy required): diffusion, facilitated diffusion. From higher concentration to lower concentration. Moving down a concentration gradient.
OR
active (energy (ATP) required). From lower concentration to higher concentration. Against the concentration gradient
16
Q
Diffusion
A
- a process where molecules move from an area of higher concentration to lower concentration until equilibrium is reached
- is passive (no energy required)
- normally occurs between the phospholipid molecules
- if it occurs through a protein molecule then it is called Facilitated Diffusion
17
Q
Osmosis
A
a process where water molecules move from areas where there is high osmotic pressure (lots of water) to areas where there is lower osmotic pressure (less water)….. (It is essentially the diffusion of water molecules).
18
Q
Three main directions of osmosis across cell membranes.
A
If the extracellular solution is:
Hypotonic (dilute): water will enter the cell
Hypertonic (concentrated): water leaves the cell
Isotonic: no net movement of water
19
Q
Osmosis in animal cells
A
In animal cells (no cell walls) eg. red blood cells:
If extracellular solution is hypotonic: Water will enter cell —> Cell will swell up —> Cell will burst (die).
If extracellular solution is hypertonic: Water will leave the cell —> Cell will shrivel up —> Cell dies.
If extracellular solution is isotonic: There is no net movement into or out of cell.
20
Q
Osmosis in plant cells
A
In plant cells (cell walls)
If extracellular solution is hypotonic (in a well watered plant): Water will enter cell and fill vacuole (cell becomes turgid)
If extracellular solution is hypertonic: Water will leave the cell, vacuole shrinks (plasmolysis occurs)
21
Q
Active Transport
A
Is the movement of substances from areas of low concentration to high concentration.
- It involves transport / membrane proteins (ie. substances move against a concentration gradient)
- is active (requires energy)
22
Q
Bulk Transport
A
Is the movement of ‘bulk’ (relatively large volumes) of substances into or out of cells. This occurs via the use of membrane bound vesicles.
There are two major processes involved:
Endocytosis: when substances enter cells via the cell membrane infolding this process is called endocytosis. If during endocytosis the substances that enter are:
- liquid this form of endocytosis is called PINOCYTOSIS
- solid this form of endocytosis is called PHAGOCYTOSIS
Exocytosis: when substances leave cells via a vesicle joining to the membrane
23
Q
Cell Surface Area to Volume ratios
A
As cells enlarge, the surface area to volume ratio decreases. Thus, as cells enlarge the rate of transport across the cell surface of required substances and wastes decreases. To increase surface area, some cells ( and even organelles) fold their surface / membranes.
The higher the surface area to volume ratio, the higher the exchange rate (eg. rate of diffusion across a cell surface).
24
Q
Role of the digestive system
A
To digest or breakdown food into smaller molecules that can be absorbed from the gut into the circulatory systems for transport to cells for use in metabolic processes (eg. cell respiration)
25
Peristalsis
The digestive system is basically a long tube along which food moves and is modified. Food moves along this tube via a process of rhythmic contractions called peristalsis.
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The 4 major processes of the digestive system
- ingestion (eating),
- digestion (physical and chemical breaking down of food),
- absorption (uptake of simple / small food substances into the circulation) and
- egestion (defecation- the removal of undigested waste eg. fibre).
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The major organs associated with the Digestive Tract (in order)
mouth, oesophagus, stomach, duodenum, small intestine, large intestine, rectum
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Mouth
Starch chemical digestion occurs here (via amylase in saliva), food physically chewed and grinded by teeth
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Oesophagus
muscular tube connecting pharynx to stomach that a bolus of food moves along
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Stomach
a sac with a muscular wall where protein digestion begins here (a protease- called pepsin in gastric juice- acidic pH)
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Duodenum
Carbohydrate, lipid and Protein digestion occurs here (involves action of amylases, lipases, protease- trypsin)...alkaline pH.
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Small intestine
absorption of many of the products of digestion (eg. glucose, amino acids (into the blood) and fatty acids (into the lymph)) across the villi lining the intestinal wall.
33
Large intestine
absorption of water
34
Rectum
storage of faeces
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The major accessory organs that add juices to the tube
liver (produces bile which emulsifies lipids producing many tiny fat droplets with larger surface area) and
pancreas (produces many digestive enzymes (lipases, amylases, a protease called Trypsin that work best in alkaline environment) in the pancreatic juice. It also produces hormones that regulate blood sugar levels (eg. insulin and glucagon)
36
Digestion
Digestion is the breaking down of food from large to small.
37
Physical (mechanical) digestion
the physical breakdown of food into smaller units by crushing or cutting actions of mouthparts or muscles. This type of digestion INCREASES surface area to volume.
3 major places:
Mouth- via the action of chewing and grinding of the food with teeth
Stomach- via the action of contractions of the stomach walls
Duodenum- via the action of bile which emulsifies lipids. (converts large fat droplets into many smaller droplets which increases the surface area)
38
Chemical digestion
the hydrolysis (catabolic breakdown reactions) of complex organic molecules into their smaller sub-units that are small enough to pass through cell membranes.
39
Amylases
Enzyme (a carbohydrase) that catalyses breakdown of Starch into maltose. Found in saliva (mouth), pancreatic juice (duodenum). Optimal action at alkaline pH.
40
Proteases
Enzymes found in gastric juice (acidic pH), Pancreatic juice (alkaline pH)
- Pepsin: catalyses breakdown of protein into pp chains
- Trypsin: catalyses breakdown of pp chains into amino acids
41
Lipases
enzyme that catalyses breakdown of lipids into fatty acids and glycerol. Found in pancreatic juice (alkaline pH)
42
Absorption
is the uptake of small nutrient units into the bodies transport systems ( cardiovascular & lymphatic). It mainly occurs across the walls of the small intestine (Ileum).
Absorption can occur via diffusion, facilitated diffusion or active transport processes.
43
Process of absorption in the ileum
The inner surface of the ileum walls is greatly folded to form finger-like projections called villi. The surface of villi cells is also folded to produce hair-like extensions called microvilli. Inside the villi are blind ending tubes called lacteals (part of the lymphatic system- that fatty acids enter) and capillary networks. Small sugar units and amino acids enter the capillaries (bloodstream) while small lipids enter the lacteals (lymph). Nutrients that enter the bloodstream then travel to the liver for processing via the hepatic portal vein.
44
The rate of absorption is enhanced at villi due to
- a large surface area (folded villi and microvilli extensions)
- thin walls (small distance)
- vascular (close to transport system).
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Cardiovascular System- role
Major role: to provide a transport system for metabolic reactants (oxygen and nutrients eg. glucose, amino acids, minerals, vitamins) & metabolic wastes (carbon dioxide and urea). It also transports substances such as hormones and antibodies.
46
Cardiovascular system: its two major circuits
Pulmonary Circuit (blood travels between the heart and lungs)…a small circuit
Systemic Circuit (blood travels between the heart and the rest of the body)… a large multi-branched circuit
47
The Heart
48
3 major components of the cardiovascular system
1. Heart (muscular pump),
2. Blood vessels (arteries, veins and capillaries) which are hollow tubes and
3. Blood (plasma, red blood cells, white blood cells and platelets)... a fluid medium.
49
The Heart and its main features
The vertebrate heart is a muscular pump that forces blood into arteries that forces blood to the lungs and also around the rest of the body.
- is a muscular pump
- Is 4 chambered. Each separated by a combination of the septum (central wall) and atrio-ventricular (AV) valves (tricuspid and bicuspid valves)
* Two receiving chambers at the top of the heart called Atria. Blood enters the chambers via veins (vena cava and pulmonary veins)
* Two pumping chambers at the base of the heart called Ventricles. Blood leaves these via arteries (pulmonary artery and aorta)
* The right side of the heart transports deoxygenated blood.
* The left side of the heart transports oxygenated blood.
50
Blood flow through the heart
1. Deoxygenated blood returns from the body organs via the vena cava vein to the right atrium
2. From the right atrium the blood moves into the right ventricle
3. The right ventricle pumps blood to the lungs via the pulmonary artery
4. In the lungs the blood becomes oxygenated
5. Oxygenated blood returns to the left atrium via the pulmonary vein
6. Blood moves from the left atrium to the left ventricle
7. It then leaves the left ventricle via the aorta to be transported all around the body to body organs
51
Blood pressure
BP is a measure of the pressure in the blood as it travels through blood vessels (Arteries) around the body. Blood pressure decreases the further the blood travels from the heart. It is recorded as two numbers: Systolic pressure over Diastolic pressure (units mmHg). eg. 120 / 80 mmHg.
Note: High Blood Pressure: often considered 140 / 90 mmHg & above (enhanced by stress, poor diet (high salt, cholesterol) , being overweight & some medications) while Low Blood Pressure is 30 mmHg lower than ‘normal’ eg. 90/60 mmHg). High BP can increase risks of Heart attacks, Stroke & Kidney Disease)
52
Blood pressure- systolic
The pressure exerted by blood in an artery resulting from ventricular contraction
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Blood pressure- diastolic
the pressure in an artery resulting from ventricular relaxation.
54
Blood Vessels
Blood travels around closed circulatory systems via tubes called blood vessels, In vertebrates there are three major kinds of blood vessels: Arteries (transport blood away from the heart), Veins (transport blood to the heart) and capillaries (link small arteries with small veins).
55
Arteries
- transport blood away from the heart
- have thick muscular walls
- normally transport oxygenated blood
- do not have valves
- transport blood under high pressure
56
Veins
- transport blood towards the heart
- have thinner walls wide diameter lumen
- normally transport deoxygenated blood
- do have valves
- transport blood under very low pressure (using the process called ‘milking’ involving alternating valve and skeletal muscle action)
57
Capillaries
- are branched networks that connect small arteries (arterioles) to small veins (venules)
- thin diameter, walls are I cell thick and are leaky
- sites of nutrient / gas / waste exchange between cells and blood
58
Blood
Blood is the fluid transport medium that takes oxygen and nutrients to tissue cells and wastes away for disposal. There are four major components of blood: red blood cells, white blood cells, platelets and plasma. Blood has many functions.
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The Plasma
a clear fluid matrix. It contains: water, salts, nutrients, hormones, wastes and various kinds of proteins (eg. fibrin, antibodies). It is a transport medium eg. carbon dioxide mainly travels via plasma as bicarbonate ions.
60
The red blood cells
are biconcave discs that have no nucleus.. They contain haemoglobin, a protein pigment that binds to oxygen and transports it to body tissues (as oxyhaemoglobin)
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The white blood cells
are large cells with a large nucleus. There are many different types (eg, macrophages, lymphocytes and neutrophils) that fight infection and provide immunity.
62
The platelets
are small and irregularly shaped cell fragments that have no nucleus. They help the blood to clot with the help of plasma proteins.
63
The Cardiac Cycle
There are two major phases in a cardiac cycle: Systole and Diastole. Systole normally refers to ventricular contraction while Diastole refers to ventricular relaxation.
1. Blood enters the Atria (via the vena cava and pulmonary arteries)
2. The SA Node (pacemaker) sends electrical impulse across the walls of the atria causing atrial contraction. This pressure increase causes the AV valves to open.
3. Blood travels into relaxed Ventricles through open AV (Atrio-ventricular) valves (tricuspid -on the right and bicuspid-on the left). The relaxed ventricles are in diastole phase.
4. AV Node (at base of right atrium) relays the electrical impulse through the septum and walls of the ventricles causing ventricular contraction.
5. The pressure increase causes semi-lunar valves to open and AV valves to close. AV valves closing causes blood turbulence (producing a LUB sound)
6. Blood travels from ventricles into the major arteries (the aorta and pulmonary artery) leaving the heart through open semi-lunar valves. Contracting ventricles are in systole phase.
7. Semi-lunar valves close preventing backflow of blood into the ventricles. (Semi-lunar valves closing causes blood turbulence producing the DUB sound)
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Lymphatic System- role and structure
Role: To provide a transport system for fat subunits, some proteins and lymphocytes. It drains fluid from the tissues and transports this fluid (lymph) in one direction from the tissues towards the heart. It also has a role in immunity.
Structure: a clear fluid called lymph (made from plasma and tissue fluid), thin walled vessels with valves called lymphatic vessels, lymph nodes clustered near body openings ( neck, groin, armpits) house the B & T lymphocytes, accessory organs such as thymus gland, tonsils, appendix
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How do substances (nutrients) leave the bloodstream and travel to body cells & where is lymph made?
1. At the tissues & capillary networks the liquid part of the blood (PLASMA ) is forced out of the capillary (they have leaky walls) into the space surrounding the tissue cells. This fluid is now called INTERSTITIAL or INTER-CELLULAR FLUID.
2. This Interstitial fluid that bathes the tissue cells then returns to the bloodstream via two methods:
i) It re-enters the capillary at the venous end of the capillary network or
ii) It enters lymphatic vessels (and is now called LYMPH) and travels via the lymph vessels to the sub-clavian veins (in the base of the neck). Here it again mixes with PLASMA of the Cardiovascular system.
ie. Plasma --------> Interstitial (Inter-cellular) Fluid ---------> Lymph -----------> Plasma
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Respiratory system- role, structure, processes
Role: To obtain oxygen (for cellular respiration) and remove carbon dioxide from the body
Structure: A system of tubes that get smaller and smaller in diameter which branch through the lungs and end in small clusters of thin walled sacs called alveoli.
Processes:
Ventilation / Breathing
Gas exchange
Cellular respiration
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Pathway of air through respiratory system
Air moves through the mouth and nose
down the pharynx and trachea
the pathway splits into two bronchi (singular, bronchus).
Each bronchus branches into a network of tubes (bronchioles) that become progressively smaller.
They finally open into bubble-like sacs, the alveoli (singular, alveolus). The total surface area of gas exchange alveoli is equivalent to that of a tennis court (about 70 square metres).
nasal cavity & mouth --> pharynx ---> larynx ---> trachea ---> lungs --> bronchi ---> bronchioles --> Alveoli
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Ventilation/breathing
Inhalation:
Diaphragm and intercostal muscles contract
Ribs move up, diaphragm moves down
Volume inside lungs is greater
Air pressure in lungs is less than outside body
Airflow is into the body
```
Exhalation:
Diaphragm and intercostal muscles relax
Ribs move down, diaphragm moves up
Volume inside lungs is less
Air pressure in lungs is greater than outside body
Airflow is out of body
```
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Gas Exchange
1. At the alveoli (lungs): gases diffuse between the air (inside alveolus) and bloodstream (capillary surrounding alveolus). Oxygen diffuses from the air to the blood stream (combining with haemoglobin to produce oxyhaemoglobin in red blood cells) and carbon dioxide diffuses from the plasma (bicarbonate ions) to the air.
2. At the tissues (across capillaries to body cells): gases diffuse between the bloodstream (capillaries) and the body cells. Oxygen diffuses from the blood (oxyhaemoglobin) to body (eg. muscle) cells for use in cellular respiration. Carbon dioxide waste diffuses from body cells into the interstitial fluid and then travels mainly in the plasma of the blood. Here it changes form and mainly travels as bicarbonate ions.
70
Features that enhance the rate of gas exchange at alveoli
large surface area (numerous & with curved shape)
moist surface
close proximity of blood capillaries (small distance to travel into transport system)
thick walls
71
Features that enhance the oxygen saturation of haemoglobin at alveoli
low temperatures
low carbon dioxide levels
low levels of DPG ( a metabolic product that competes with oxygen for space on haemoglobin molecules)
low acidity (slightly alkaline conditions)
72
Cellular respiration
Occurs in all eukaryotic cells (all of the time…day and night) at the mitochondria. In this metabolic process the chemical potential energy contained in large organic molecules (eg. glucose) is converted into a more readily used form of energy (ATP- Adenosine Triphosphate) eg. 1 glucose produces 36-38 ATP molecules.
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Excretion in Animals
The removal of metabolic waste products. (Metabolism is the chemical activity / reactions that occur within cells) (eg. carbon dioxide, urea, Bile pigments).
Lungs (alveoli / capillary network)
Exhalation
Carbon dioxide, Water
Skin (sweat glands)
Sweat production
Salt, Urea, Water
Liver (lobules)
Bile secretion
Bile pigments
Kidneys (nephrons)
Urine production
Urea, Salt, (Ions), Water
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Human Urinary System- role
1. Maintaining Water Balance
2. Maintaining Salt / Ion Balance
3. Eliminating Nitrogenous Wastes (produced when proteins breakdown):
- Ammonia (very toxic): (NH3) very toxic to animal cells formed from the breakdown of amino acids.
- Urea (lower toxicity): Water soluble nitrogenous excretory product of protein breakdown. Mammals and amphibians excrete urea in their urine.
- Uric Acid (a paste of very low toxicity): A complex non-toxic nitrogenous excretory product, present in reptiles and birds. It is excreted as a thick, white paste (bird poop) it helps animals having to dilute the urea or ammonia in water (helping in water conservation.)
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major components of the urinary system
The organs of the urinary system include the kidneys, renal pelvis, ureters, bladder and urethra.
renal blood vessels, kidney, renal pelvis, minor calyx, renal cortex, Renal medulla, major calyx, ureters, bladder, sphincters, Urethra
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Kidneys- role
To filter (clean) blood and to maintain salt (ion)/ water balance.
The functional units of the kidney that enable this to be achieved are called Nephrons (1-2 million per kidney).
77
How does blood move to/through/from the kidneys?
Blood travels to the kidneys via:
Aorta --------> Renal Artery -------->
Blood travels through the kidneys via:
Renal Arterioles --------> Glomerulus --------> Nephron (peritubular) capillaries --------> Renal Venules
Blood travels from the kidneys via:
Renal Veins --------> Inferior Vena Cava
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Structure of kidneys
The major zones of of the kidney are:
Capsule: an outer coating of tough connective tissue
Cortex: the outer part of the kidney
Medulla: the middle zone-comprised of triangular shaped lobes of tissue called 'pyramids'
Renal Pelvis: a funnel shaped collecting chamber connected to the ureter, before it leaves the kidney
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Glomerus (nephron)
a capillary knot found in the Bowman's capsule from which fluid & dissolved solutes are forced out of due to high blood pressure (ultrafiltration of blood) (“Sieve”).
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Bowmans capsule (nephron)
collection area for filtrate (forced out of glomerulus).
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Proximal convoluted tubule (nephron)
the tubule of the kidney nephron arising from teh Bowman's capsule and leading to the Loop of Henle; responsible for the reabsorption of water, ions (sodium chloride) & all organic nutrients (glucose).
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Loop of Henle (nephron)
Area between proximal and distal convoluted tubules (U-shaped tube) whereby high salt concentration in the tissues is maintained, resulting in diffusion of water from the filtrate to the surrounding blood capillaries.
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Distal convoluted tubule (nephron)
Whereby reabsorption of water & ions (sodium, potassium, phosphate and calcium ions) occurs under the control of hormones.Secretion of ions, acids, drugs and toxins; further
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Collecting tubule (nephron)
Receive fluid from many nephrons – variable reabsorption of water due to ADH.
85
Capillary network (nephron)
Where water, organic nutrients & ions are reabsorbed.
86
Glomerular Filtration (process in nephron)
Blood pressure forces liquid part of blood (plasma) across glomerulus wall to produce filtrate collected in the Bowmans capsule. Solute molecules are carried by water molecules & become part of the filtrate (cells and larger plasma proteins eg. fibrin & blood cells remain in blood stream).
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Selective reabsorption (process in nephron)
Some water and solutes (salts, glucose) that are useful to the body are selectively reabsorbed along the tubule from the filtrate back into the blood (use simple diffusion, osmosis & carrier proteins).
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Secretion (process in nephron)
Transport of toxic solutes are secreted in the DCT into the tubular fluid. Secretion can be the primary method of excretion for some toxic compounds / ions (eg. H+ ions), including many drugs (eg. Antibiotics).
89
Water Balance
is maintained by the action of the hormone ADH (Anti Diuretic Hormone)
On a cool or low exercise day (low sweat production): ADH production will be low, therefore less water will be reabsorbed from the tubule into the bloodstream (peritubular capillary) and more water will remain in the tubule. Thus urine volume will be high
On a hot day or after exercise (high sweat production): ADH production will be high, therefore more water will be reabsorbed from the tubule into the bloodstream (peritubular capillary) and less water will remain in the urine in the tubule Thus urine volume will be low.
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Salt Balance
is maintained by the action of the adrenal gland hormone called aldosterone which increases salt (& water) reabsorption (in the distal convoluted tubule)
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Central Nervous System
containing the brain and spinal cord(both are protected by bone, meninges (membranes) and cerebrospinal fluid)
The brain has 5 major sections (has grey matter on outside):
- the cerebrum: associated with thinking / reasoning / memory / emotions
- the thalamus: relay centre for sensory messages
- the hypothalamus: controls autonomic (involuntary) NS and links NS with endocrine system. Regulates, temp, appetite, thirst, sleep.
- cerebellum: associated with co-ordination / movement / balance
- brain stem: connects brain / spinal cord and regulates breathing rate & heart rate.
- The spinal cord (has grey matter on the inside and white matter on the outside) connects to the brain stem (approx. 45cm long).
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Peripheral Nervous System (PNS)
Containing the:
a. cranial nerves (12 pairs that connect to the brain and innervate the facial / neck region)
b. spinal nerves (over 30 pairs that connect to the spinal cord through spaces between adjacent vertebrae).
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What is nervous tissue composed of?
Nerves are composed of many nerve bundles each containing numerous nerve cells called neurones.
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How are neurones arranged?
End to end there is a space between adjacent neurones called a Synapse.
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What are the major parts of neurones?
All neurones have three major parts:
Dendrites – send messages in towards the cell body
Cell body (soma) – contains nucleus and most organelles of the cell
Axon – sends messages in one direction only (away from cell body)
Myelin sheath - insulates the axon so action potential passes quicker. Made of Schwann cells
Nodes of Ranvier - gaps in the myelin sheath which speeds up the action potential.
Axon terminal - branched ends of the axon
Synapse - gap between neurones.
96
What are the major types of Neurones?
three major groups of neurones:
Sensory: send messages from receptors towards the central nervous system. Located in PNS
Association: send messages between motor and sensory neurons (CNS)
Motor neurones: send messages away from the central nervous system to effector organs (muscles and glands) (PNS)
97
How do these different kinds of neurones work together?
Sensory, connecting and motor neurones work together in Reflex Arcs. Reflex arcs produce very rapid, unconscious responses.
The major steps involved in a reflex arc:
1. A stimulus is detected by a sensory receptor (eg. in skin) which transmits a message (an electrical impulse) along a sensory (afferent) neurone into the C.N.S (spinal cord).
2. Within the spinal cord this message is transferred (via a synapse) to a connecting (inter-) neurone (in the grey matter of the spinal cord).
3. The message is then transferred (via a synapse) to a motor (efferent) neurone which transmits this message away from the C.N.S to an effector organ (a muscle or gland).
4. The effector responds (eg. muscle contracts).
5. After this response occurs a message is then sent up the spinal cord to the brain, then the person ‘feels’ the stimulus / pain.
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Electrical messages/Action Potential (Impulses)
The outside of neurone cell membranes are normally positively charged. A rapid sequential movement of charged ions across the cell membrane (Na+ ions into the axon of the cell) causes the outer membrane to become negatively charged. This region of negative charge moves in one direction along the neurone (as an impulse).
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Chemical messages (neurotransmitters at synapses).
Two neurones do not make direct contact. Where they meet, there is a very small gap called a synapse.
Special neurotransmitter chemicals (eg. Acetylcholine) are released by the synaptic end bulbs into the synapse. These chemicals then cross the synapse and are detected by receptors in the membrane of the next neurone.
These stimulated receptors initiate a new impulse and this membrane releases specific enzymes that deactivate the neurotransmitter (eg. cholinesterase)
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Steps of chemical transmission
1. An electrical impulse travels along an axon.
2. This triggers vesicles in the synaptic knob to move to the pre-synaptic membrane and release chemical messengers called neurotransmitters (eg: Acetylcholine).
3. These chemicals diffuse across the synapse (the gap) and bind with receptor molecules on the membrane of the next neuron.
4. The receptor molecules on the second neuron bind only to the specific chemicals released from the first neuron. This stimulates the second neuron to transmit the electrical impulse.
5. Enzymes (eg. cholinesterase) secreted by the second neurone (post synaptic membrane) break down the neurotransmitter.
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Endocrine System
This system is a slow acting system with relatively long lasting effects.
Involves chemical messengers (hormones) made by ductless endocrine glands that travel through the general blood stream and act on target cells.
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The endocrine system regulates what long-term processes?
Homeostasis
Growth
Development
Reproduction
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What is the endocrine system composed of
Endocrine glands: A variety of endocrine (ductless glands) and organs that contain tissues that secrete small quantities of hormones. These chemicals (often types of proteins) travel via the blood stream around the body to ‘target’ cells / tissues.
Target cells: have specific receptors on their cell membranes that specific hormones bind to. Causing changes inside those cells.
Hormones: are largely slow acting and have long lasting effects (with exceptions of the hormones: adrenalin and oxytocin)
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The Pituitary: the master gland
The master gland of the body is called the pituitary gland (located at the base of the brain) because it releases many hormones, a number of which stimulate other endocrine glands or endocrine organs.
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The hypothalamus integrates activities of the nervous and endocrine system in three ways:
Secretes hormones that influence the pituitary gland
Acts as endocrine organ, producing ADH and oxytocin
Contains autonomic centres (homeostasis)
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What are the major glands / organs of the endocrine system and their products?
Pituitary: Oxytocin, Antidiuretic Hormone (ADH)- Water reabsorption in Kidney nephrons
Thyroid: Calcitonin- Blood Calcium
Para thyroid(s): Parathyroid Hormone- Blood Calcium
Adrenal(s): Adrenalin- Heart Rate and Breathing Rate
Pancreas: Insulin, Glucagon- Blood Glucose
Ovaries (females)- Oestrogen, Progesterone- Lining of uterus thickness, hip widening & breast development at puberty (secondary sexual features), Maintains uterine lining
Testes (males): Testosterone- Voice deepening, pubic hair,
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Positive Feedback
Positive feedback intensifies any initial move away from normal (therefore does not maintain homeostasis and may result in death of the organism).
Usually control infrequent events that are self perpetuating.
Do not control events which require continuous adjustments.
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Negative Feedback
Negative feedback opposes any initial move (of a factor) away from ‘normal’ (therefore brings conditions back towards ‘normal’).
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representation of the stimulus–response model
Stimulus – receptor – coordinating system – effector – response
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Plants are a very important group of living things because they are photoautotrophs (producers that photosynthesise) and thus:
Produce organic molecules (eg: glucose) and are at the base of virtually all food chains (are photoautotrophs).
Produce oxygen (which is used then by many cell types during cellular respiration)
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Equation for cellular respiration
C6H12O6 + 6O2 → 6CO2 + 6H2O
Glucose + Oxygen → Carbon dioxide + Water + energy (ATP)
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Plant Cells require gases for the process of:
Photosynthesis (where carbon dioxide is required & oxygen is produced)
Respiration (where oxygen is required & carbon dioxide is produced)
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Gases enter and leave plants in a number of major ways:
STOMATA - gases (and water vapour) enter & leave leaves (& some stems) via small epidermal structures called stomata. These structures are composed of two Guard cells surrounding a pore called a stoma. Gases diffuse through the stoma and intercellular spaces in the spongy mesophyll layer (& vice versa).
LENTICELS - gases enter & leave lower stems / trunks of some plants that inhabit waterlogged soils (e.g. Mangrove & Rainforest trees) via clusters of loosely packed cells called lenticels.
ROOT HAIRS - gases (& water / mineral ions) enter roots from air spaces in the soil via small epidermal extensions called root hairs.
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Leaf structure (watch video)
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Stomata (role and structure)
Role: Stomata control the movement of gases in and out of a leaf, making carbon dioxide available for photosynthesis, and controlling the loss of water from the leaf through transpiration.
Each pore or stoma is surrounded by two sausage-shaped guard cells, which change shape to control the size of the stomatal aperture. In the majority of leaves with an upper and lower surface (dorsiventral) like this dicot, most stomata occur in the lower epidermis. They are usually evenly distributed in the leaves of monocots.
Function: Epidermis is relatively impermeable which reduces water loss but also reduces gas exchange. These adjustable pores found in the epidermis, called stomata, overcome this problem. Stomates allow for gas exchange while preventing excess water loss.
They allow carbon dioxide in for photosynthesis and oxygen out. They also allow water out via transpiration.
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Transport in vascular plants - Xylem and Phloem
XYLEM - composed of large, thick walled vessel elements and tracheids which transport water and mineral ions upwards from the roots, through the stems to the leaves. Mature Xylem contains spiral thickenings and is dead tissue. Movement of materials through the xylem is referred to as the transpiration stream.
Phloem - composed of smaller, thin walled sieve tubes and their companion cells. Sieve tubes transport organic molecules (eg. carbohydrate) away from the leaves to the rest of the plant (sinks eg. fruits, roots). Mature Phloem contains living companion cells (needed for the active transport of organic molecules). Movement of materials in phloem sieve tubes is called translocation.
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Transpiration (occurs in xylem)
Transpiration is the process by which plants absorb water through the roots and then give off water vapour through the stomata in their leaves.
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What two strong forces act on water molecules in the xylem for transpiration to occur?
Cohesion acts between the water molecules, holding them together.
Adhesion acts between the water molecules and the cellulose of the cell walls.
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What enhances the force of adhesion
The vessels and tracheids are very narrow in relation to their length, therefore there is a large surface area in contact with the water. This enhances the force of adhesion. The water column in the xylem has a small diameter so the forces of cohesion between the water molecules are also great.
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Pushing of the xylem sap occurs via:
root pressure. Root cells expend energy to pump minerals into the xylem. Minerals accumulate in the xylem sap thus lowering the water potential. Water therefore flows into the xylem sap (via osmosis because it is following the higher mineral concentration inside the root), generating a positive pressure that pushes the fluid up the xylem.
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Factors that influence rate of transpiration
1. LIGHT
Stomata usually open in the light and close in the dark.
2. TEMPERATURE
An increase in temperature increases the rate of transpiration.
3. HUMIDITY
An increase in humidity causes a decrease in transpiration. This is due to a decreased diffusion gradient between the intercellular spaces and the atmosphere, which reduces evaporation.
4. WIND
Wind increases transpiration by the removal of water vapour around the stomatal pore. Because the water vapour is removed, the concentration gradient is maintained, and water continues to evaporate.
5. SOIL WATER
If the supply of soil water is reduced, the solute concentration of the soil will increase. This results in a decrease in the amount of water absorbed by the roots and a decrease in the transpiration rate.
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Translocation
Translocation is the movement of organic molecules throughout the plant. It occurs in the sieve tubes of the phloem and can take place in any direction (from leaves to roots, leaves to apex etc).
Molecules, including sugars and amino acids, produced in the photosynthetic cells in the leaf are transported to the non-photosynthetic cells (e.g. actively growing points such as the apex, branches and root tips). Excess glucose can be stored in roots, stems and leaves for future use (e.g. carrots and potatoes).
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