B2 Topic 3: Common Systems

B2 Topic 3: Common Systems

Fossils and evolution
Fossils are preserved remains of organisms that lived on Earth millions of years ago.
Collection of fossils from different periods in Earth’s history is known as the ‘fossil record’.
Studying fossils through different periods can show how organisms have changed i.e. how they have evolved.
Gaps in the fossil record
·  Soft-bodied organisms decay
·  Soft tissue decays
·  Hard parts of organism can be destroyed
·  Fossils can be destroyed/find only parts
·  Fossils are buried deep and so have yet to be found.
Pentadactyl limb
·  All vertebrates have same 5-fingered limb structure aka pentadactyl limb
·  Humerus
·  Radius
·  Ulna
·  Carpels
·  Phalanges/fingers
·  From fossils we know organisms (some limbless) had a pentadactyl limb millions of years ago
·  Suggests all vertebrates evolved from a common ancestor.

·  The pentadactyl limb has evolved differently in different vertebrates, to adapt to different ways of living and moving
Growth
Growth is an increase in size, length or mass. In babies head circumference can be measured.
Percentiles can be used to compare a certain characteristic (e.g mass) against the total population
o  the 50th percentile is the median value of the sample
Blood
Made of four main components
Plasma (55%)
·  Yellow liquid
·  Transports dissolved substances e.g. carbon dioxide, hormones, food substances.
Red blood cells (45%)
·  Biconcave disk to increase surface area and have no nucleus
·  Contain haemoglobin
·  RBC pick up O2 at alveolus and it binds to haemoglobin forming oxyhaemoglobin.
·  haemoglobin + oxygen ↔ oxyhaemoglobin
White blood cells (>1%)
·  Part of immune defence systems
·  Make antibodies which bind to and destroy microorganisms
·  Produce antitoxins
·  Destroy foreign cells by engulfing them this is called phagocytosis.
Platelets (>1%)
·  Only fragments of cells
·  Important role in clotting blood
·  Forms scab when cut dries (stopping microbes entering body)
/ Growth in plants
Plants have special areas called ‘meristems’ found on the tips of roots and shoots
·  these are the sites of plant growth
Plants will continuously grow
Processes contributing to plant growth
·  Cell division: cells in meristems keep dividing constantly (each division doubles the number of cells)
·  Elongation: once the cells have divided, they get longer – this is called ‘elongation’
·  Differentiation: as a plant continues to grow, the older meristem cells start to develop into specialised cells.
·  Meristems can differentiate into any plant cell
Growth in animals
Involves cell division, but in animals growth stops when adulthood is reached.
In an animal, cells that can differentiate to form many different types of specialised cells are called stem cells:
·  Embryonic stem cells can differentiate and form almost any type of cell in the body
·  Adult stem cells can only develop into a limited range of cells
i.  This is why most animals can’t re-grow a damaged limb or body part, but plants can grow new shoots, roots and leaves

The heart
Function: Pump blood around body
·  Blood coming in from the tissues is low in oxygen (‘deoxygenated’)
·  It is pumped by the heart to the lungs where haemoglobin in red blood cells picks up oxygen (blood becomes ‘oxygenated’
·  This oxygenated blood returns to the heart where it is then pumped around the body to the tissues and cells (so that cells receive oxygen for use in aerobic respiration)
Structure:

Veins carry blood IN to the heart
·  Vena cava – body’s biggest vein – brings blood into the right atrium from the rest of the body
·  Pulmonary vein – brings blood to left atria from lungs
Arteries carry blood AWAY from the heart
·  Aorta – body’s main artery – carries blood from left ventricle to whole body
·  Pulmonary artery – carries blood from right ventricle to lungs.
How blood travels through the heart
1.  Blood enters right atrium from body
2.  Atria contract
3.  Blood pushed down to right ventricle, valves close behind.
4.  Ventricles contract
5.  Blood pushed through pulmonary artery to lungs, valves close behind.
6.  Blood picks up oxygen
7.  Pulmonary vein brings oxygenated blood back to heat, blood enters left atrium
8.  Atria contract, blood is pushed to left ventricle. Valve closes behind.
9.  Ventricles contract blood is pushed out of the left ventricle through aorta. Valve closes behind.
·  Valves – prevent backflow
·  Heart is made of cardiac muscle which contracts and relaxes
Heart thickness
·  Atria have relatively thin walls compared to ventricle because only pumping blood down to ventricles.
·  Right ventricle has thicker wall than atria as blood is pumped to lungs but thinner walls than left ventricle.
·  Left ventricle has thick walls as pumps blood around the whole body.
The circulatory system
·  Cells working together for a job are tissues e.g. muscle
·  Tissues working together for a job are organs e.g. heart
·  Organs working together for a job are an organ system e.g. circulatory system
Blood vessels
Arteries carry blood away from heart
·  Blood in arteries under high pressure
·  Have strong, thick muscular walls to cope with pressure.
Veins carry blood towards the heart
·  Blood moves slowly at low pressure
·  Have wide, large passage for blood to flow and thin walls.
Capillaries allow substances to diffuse in and out of blood/in and out of cells.
·  Very think walls to help diffusion / The digestive system
Digestion is breaking down large insoluble food molecules into smaller soluble ones.

Alimentary canal is the route the food takes from the mouth to the anus.
Mouth – food enters body here
·  Mechanical digestion – teeth break food into smaller pieces and tongue rolls food into bolus
·  Chemical digestion – saliva adds enzyme amylase which digests carbohydrates
·  Saliva also lubricates bolus.
Oesophagus
·  Muscular tube that connects mouth to stomach.
·  Food is pushed through the oesophagus by peristalsis
·  Peristalsis – muscles contract and relax in waves pushing food down.
Stomach
·  Muscular bad that makes stomach acid and some enzymes
·  Stomach acid kills bacteria and aids digestion
·  Enzymes pepsin and trypsin work
Small intestine
·  long, coiled, muscular tube
·  Contains many digestive enzymes
·  Soluble food molecules absorbed into blood here
·  Contains villi which increase the surface area and have a large capillary network to encourage diffusion
Large intestine
·  Undigested food passes into here
·  Wide, thin-walled tube
·  Water diffuses back into blood, leaving waste behind
Anus
·  Waste is passed out of the body as faeces
Pancreas
·  Makes digestive enzymes and releases them into first part of small intestine
Liver
·  Once digested food passes into blood the liver processes it and
·  Some molecules broken down further
·  Some are built up into larger molecules again
·  Liver also makes bile. Bile emulsifies fats and makes them easier to digest.
Gall bladder
·  Stores bile
·  Releases bile into small intestine when needed. / Probiotics and prebiotics
Bacteria in the digestive system that have health benefits are called ‘beneficial’ bacteria.
Probiotics:
·  contain live ‘beneficial’ bacteria – these are usually Lactobacillus and Bifidobacteria, which produce lactic acid in the gut.
·  The makers of foods containing probiotics (e.g yoghurt) claim that they will make you healthier by…
o  improving your digestive system
o  helping your body protect itself against disease
o  reducing allergies
·  However…
o  A study in 2010 by the European Food Safety Agency concluded that there wasn’t enough evidence to support these health claims
Prebiotics:
·  they provide food for the beneficial bacteria in the gut and encourage their growth
·  Tomatoes, bananas, onions and asparagus all contain oligosaccharides – a common form of prebiotic
Plant Stanol Esters
·  oily substances found in plants
·  these oily substances can stop the small intestine absorbing cholesterol, lowering cholesterol levels in the blood
o  High cholesterol levels in the blood are linked to raised risk of heart disease
foods that claim to make people healthier (e.g yogurt) are called ‘functional foods’
Digestive enzymes
Carbohydrase enzymes break down carbohydrates into sugars
e.g. Amylase present in saliva and SI breaks down starch into simple sugars.
Protease enzymes break down proteins into amino acids
e.g. pepsin which is present in the stomach. It works in acidic condition.
Lipase enzymes break down lipids (fats) into glycerol and fatty acids.
·  Fats are insoluble so form large globules, these have a small surface area and are hard to digest.
·  Bile breaks down these globules into tiny droplets, increasing the surface area and making them easier to digest.
Villi
The lining of the small intestine contains millions of folds called villi. Villi help absorption into blood because:
1.  Large surface area:
2.  Large capillary network:
3.  Single layer of cells: