Biology

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Biology 3 Topic 1

The menstural cycle is controlled by hormones.

FSH - follicle stimlulating horomone.

  • Causes a follicle (an egg and its surrounding cells) to mature in one of the ovaries.
  • Stimulates oestrogen production.

Oestrogen -

  • Causes the lining of the uterus to thicken and grow.
  • A high level stimulates an LH surge (a rapid increase).

 

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Biology 3 Topic 1

Menstural Horomones

If a fertalised egg implants in the uterus (the woman becomes pregnant) then the level of progesterone will be high to maintain the lining on the uterus lining during pregnancy.

The uterus lining has a thick spongy layer of blood vessels, this blood supply allows the placenta to develop.

The placenta supplies the baby with oxygen, glucose and nutrients and removes the waste products (like urea and carbon dioxide).

The baby needs oxygen, glucose and nutrients in order for it to grow.

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Biology 3 Topic 1

NEGATIVE FEEDBACK - MENSTRUAL CYCLE

During the menstrual cycle, the level of feedback controls the different hormones in the blood.

FSH is controlled by negative feedback:

FSH stimulates the ovary to release oestrogen.

Oestrogen inhibits futher release of FSH from the pituitary gland (in the brain).

After FSH has caused a follicle to mature, negative feedback keeps FSH levels low.

This makes sure no other follicles are matured.

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Biology 3 Topic 1

FERTILITY TREATMENT

Hormones can be used to increase fertility.

When women have low levels of FSH, their eggs cannot mature.

This means no eggs are released and the woman cannot get pregnant.

The hormones FSH nad LH can be injected by these women to stimulate egg release in their ovaries.

PROS - It helps a lot of women to get pregnant when they cant naturally.

CONS - It doesnt always work, some women have to do it many times which can be expensive. Also too many eggs could be stimulated resulting in multie pregnancies (twins etc).

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Biology 3 Topic 1

IVF -

IN VITRO FERTILISATION

  • Collects eggs from the woman.
  • Fertilises eggs with mans sperm.
  • Grow into embryos.
  • When the embryos are tiny cells, transfer into womans uterus (womb).
  • FSH and LH are given before the collection to stimulate egg production.

PRO - Fertility treatment can given an infertile couple a child.

CONS - Some women have a strong reaction to hormones. (leads to vomitting, abdominal pain) Could lead to increased risk of cancer due to the hormonal treatment.                                       Multiple births can happen if more than one embryo grows into a baby. Could mean higher risk for miscarriage.

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Biology 3 Topic 1

DONATING EGGS FOR IVF-  Can be done with a donor egg.

PROS - It allows a woman who cant produce eggs to have a baby. Using a donated egg can prevent the risk of passing a genetic disorder from the mother.

CONS - It can be emotionally difficult for the family knowing that the child has a different genetic mother.

SURROGATE MOTHER - a woman who carries a baby for another couple.

IVF is used to produce an embryo, either using the egg and sperm from the couple or using a donor egg and sperm.  This is then implanted into the surrogate mothers uterus where the baby will grow.  After giving birth, the woman will give the baby to the couple who asked her to be a surrogate.

PROS - allows couples to have children if they cannot.

CONS - Surrogate mother is legally the mother until they adopt the child meaning she has the right to keep the child.

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Biology 3 Topic 1

X and Y chromosomes:

  • 22 matched pairs of chromosomes in every human body CELL.
  • The 23rd pair are either labelled XY or **.  This determines if you are a boy or a girl.

XY = BOY

** = GIRL

When making a sperm, the X and Y chromosomes are drawn apart in the first devision of meiosis.

There is a 50% chance each sperm gets an X chromosome and 50% chance it gets a Y chromosome.

A similar thing happens when making eggs but the orginial has two X chromosomes so all the eggs have one X chromosome.

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Biology 3 Topic 1

KIDNEY

The kidneys are excretion organs.

3 MAIN ROLES OF THE KIDNEYS:

  • Removal or urea from the blood - urea is produced in the liver from the breakdown of amino acids.
  • Adjustment of ion levels in the blood.
  • Adjustment of water content in the blood.

This happens by filtering stuff out of the blood at high pressure and then reabsorbing the useful things. The end product is urine.

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Biology 3 Topic 1

KIDNEYS

Nephrons are the fileration units for the kidney. 

Ultrafilteration - A high pressure is buuilt up which squeezes water, urea, ions and glucose out of the blood and into the bowmans capsule.  The glomerulus and the bowmans capsule act like filters so big moleucles like proteins and blood cells are not squeezed out and stay in the blood.

Reabsorption - A the liquid flows along the nephron, useful substances are reabsorbed. All the glucose is selevctively reabsorbed and is moved out of the nephron back into the blood, against the concentration gradient.   Sufficient water is reabsorbed according to the level of the hormone ADH.  The process of maintaining the right water content in the body is osmoregulation.

Releases of Waste - Urea and excess water are not reabsorbed.  They continue out of the nephron, into the ureter and down the bladder as urine.  Urine is released through the urethra.

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Biology 3 Topic 1

Sex Linked Genetic Disorders

A characteristic is sex linked if the allele that codes for it is located on a sex chromosome.

The Y chromosome is smaller than the X chromosome and carries less genes, so most genes on the sex chromosome are only carried on the X chromosome.

Because men only have one X chromosome, they often have one allele for sex linked genes.

Because men only have one X chromosome, the characteristic of the allele is shown even if it is recessive. This means it is more likely for men to show recessive characteritics for genes that are sex linked.

Disorders caused by faulty alleles located on sex chromosomes are called sex linked genetic disorders. 

Colourblindness and haemophillia are examples of sex linked genetic disorders.

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Biology 3 Topic 1

Growth of Bacteria

Bacteria reproduce by splitting in two, so the numbers double at regular intervals. This means their growth is exponential. At the start, there is only a handful of bacteria but soon there will be millions of them.  So if bacterium gets into your body, an infection can develop really fast, before the immune system has a chance to respond.

Pasteur showed, in the 19th century, that diseases did not just appear, but there are microbes in the air which cause diseases and decomposition. 

Experiment:  Heat 2 flasks of broth then leave open, one flask should have a curved neck so the bacteria in the air would settle around the loop and not get into the broth. This broth will stay fresh, but the other one didnt.  This showed that it is the microbes that caused the broth to go off, not the air.

Pastuer invented the process of 'pasteurisation' which is where you heat something up to 70 degrees C and then cool it.  This kills any bacteria and makes it safe to eat.

Any experiment done to reduce contamination is called ASEPTIC TECHNIQUE.

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Biology 3 Topic 1

Resazurin is a dye that is sensitive to oxygen.  When there is oxygen present, it is blue, when there is not as much oxygen present, it turns lilac, then mauve, then pink, then colourless.

Microorganisms use up oxygen when they respire. The more there are, the more oxygen is used up.

Resazurin can be used to monitor the growth of microorganisms. The more microorganisms there are, the greater the colour change there will be. 

This allows us to look at how different conditions affect the growth of bacteria.

EXAMPLE

Pour 10cm of fresh milk into 3 test tubes (label 1 2 and 3).  Store tube 1 at a temperature of 3 degrees, tube 2 at 10 degrees and tube 3 at 25 degrees.  Record the colour of the dye in the tubes at set intervals (after 0 hours, then 24, then 48, then 72 etc).  Record the results. Tube 1 should have changed colour the least meaning the growth of bacteria is slowest at 3 degrees and tube 3 should have changed colour the most meaning the growth of bacteria is fastest at 25 degrees.  This suggests that storing milk in the fridge rather than room temperature will slow the growth of bacteria.

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Biology 3 Topic 1

The Immune System

Once microorganisms enter your body, they will reproduce rapidly if not destroyed.  The immune system and white blood cells will destroy these for us.  White blood cells travel around in your blood and get into every part of you, patrolling for microorganisms.  There is a certain white blood cell, B-lymphocytes, that release antibodies when they come accross a microorganism.

Every pathogen has unique molecules on the surface area of its cells - no two species has the same one.  These molecules are called anitgens.  When the B-lymphocytes comes across a foreign anitogen, they start to produce proteins called antibodies which lock on and kill the invading cells. The anitbodies produced are specific to that pathogen and wont lock on to other pathogens. Antibodies are then produced rapidly and flow all around the body to kill and similar bacteria or virsuses.  

When a pathogen enters the body for the first time, the response is slow because there arent many B-lymphocytes that can make the anitbody needed to lock on to the antigen.  The body will produce enough antibodies to overcome the infection but the person will already be showing signs of the illness.  After being exposed to an antigen, a memory lymphocyte is formed which remains in the body for a long time, attacking and simillar pathogens to the orginal one, making your body immune to the illness.  This means any 2nd infection, the immune system can act quickly and get rid of the anitgen before symptoms start to show.

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Biology 3 Topic 1

Immunisation

Immunisatioon involves injecting dead or inactive microorganisms into the body.  These are antigenic (contain antigens) so even though they are harmless, your body makes antibodies to attack them.  These antigens also trigger memory lyphocytes to be made. If live microorganisms of the same type appear after the injection, they will be killed off by the antibodies which has already been developed against them.

Edward Jenner invented the first vaccine.  It worked against a disease called small pox.  Edward Jenner knew that people who had cow pox didnt catch small pox.  In 1796,  he took a bit of puss from a milk maid who had cow pox (as they were most common for it) and injected it into an open wound of 6 year old James Phipps.  James Phipps was a bit poorly but became well after a few days.  A few weeks later, Jenner took some puss from a patient who had small pox and again, put it into an open wound of James Phipps.  The boy did not catch small pox.  The cow pox antigens triggered the boys B-lymphocytes to produce antibodies.  Because small pox has the some of the same anitgens as cow pox, when the boy was infected with small pox, his immune system quickly produced antibodies to stop the disease from getting in.

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Biology 3 Topic 1

Pros and Cons of Immunisation

PROS: 

  • Big breakouts of diseases, called epidemics, can be prevented if a large percentage of the population are immunised.  Even the people who are not immunised to the disease are unlikely to catch the disease as there are less people able to pass it on to.
  • Some illnesses, like small pox, can be completley wiped out by immunisation.

CONS

  • Immunisation does not always work. 
  • Sometimes you can have a bad reaction to vaccine (swelling, fever etc).  This is very rare though.
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Biology 3 Topic 1

Monoclonal Antibodies

Antibodies are produced by B-lymphocytes.

If you found a really useful antibody, you would want to make lots of clones of it.

To do this, you would have to fuse together tumour cells and B-lymphocytes (tumours split and grow easily) to make the perfect antibody.  Once these are fused together, the new cell is called a hybridoma. Hybridoma cells divide really quickly and produce lots of indenitcal antibodies, called monoclonal antibodies.  Monoclonal antibodies bind to anything.  They are useful because they will only target that specific molecule.

Monoclonal Antibodies are used in pregnanct tests.  A hormone is found in women only when they are pregnant.  The bit of the stick you wee on has some antibodies with blue beads attached.  The test ***** also has some antibodies stuck onto it so they cant move.  If youre pregnant and you wee on the stick, the hormones binds to the antibodies on the blue beads. The urine moves up the stick, carrying the hormones on the beads. The beads and hormone bind to the antibodies on the *****. So the blue beads get stuck on the *****, turning it blue. If you are not pregnant, the urine still moves up the stick, carrying the blue beads but nothing sticks to it so it doesnt turn blue.

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Biology 3 Topic 1

Monoclomal Antibodies can also stick to cancer cells.  Different cells in the body has different antigens on their cell surface so you can make monoclomal antibodies that will bind to specific cells in the body.  Cancer cells have antigens on their cell membranes that arent found on normal body cells.  Theyre called tumour markers.  In the lab, you can make monoclomal antibodies that will bind to these tumour markers.  They can be used to help diagnose or treat cancer.

 Diagnosing Cancer:  The antibodies are labelled with a radioactive element.  The labelled antibodies are given to a patient through a drip.  They go into the blood and get carried around the body.  When the antibodies come into contact with the cancer cells, they bind to the tumour markers.  A picture of the patients body is taken with a special camera which detects radioactivity.  Anywhere there is a cancer cell, a bright dot will appear.  This shows doctors how big the cancer cell is, where it is located and whether it is spreading.

Targeting Drugs to Cancer Cells: An anti-cancer drug is attatched to a monoclonal antibodies and given to the patient through a drip. The anitobodies will target the cancer cells because they are only bind to the tumour makers.  The drugs kills the cancer cells and leave the normal ones.

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Monoclomal Anitbodies are also used to find blood clots.

When blood clots, proteins in the blood join together to form a solid mesh.

Monoclomal antibodies have been developed that bind to these proteins.  

You can attach a radioactive element to these antibodies.  

If you inject them into the body and take a picture using a camera that picks up radiation, the picture will have a really bright spot where the blood clot is.  

This is useful because then you can find a potentially harmful blood clot and get rid of it before it harms the patient.

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Biology 3 Topic 1

Drugs:

Plants produce a variety of chemicals to defend themselves agasinst pests and pathogens.  Some of these chemicals can be used as drugs to treat human diseases or relieve symptoms. A lot of our current medicines were descovered by studying plants used in traditional cures.  

Aspirin: used to treat pain and lower fever.  Found in the leaves and bark of a willow tree.

Taxol: Anti cancer drug.  Comes from the bark of a Pacific yew tree. Discovered when scientists were looking for plants for treatments.

Quinine: Comes from a South American cinchona tree.  For years, it was the main treatment against malaria.

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Biology 3 Topic 1

Pests can rapidly reduce crop yeilds.

A lot of crops are lost each year because of pests such as insects, weeds and pathogens.

Different pests reduce crop yeilds in different ways:

  • Fruit flies - feed on fruit so can ruin fruit crops.
  • Weeds - grow near plants and compete for the nutrients in the soil, if the plants dont get enough nutrients, they wont grow as well and the crop yeild will be much lower.
  • Pathogens - energy is taken away from the crops, so there is less energy for apples, wheat and carrots to grow so the yeild is lower.  Sometimes, whole fields of plants produce no food at all.

Pests also add to the cost of producing food as money must be spent on pesticides and disease resistant or insect resistant crops.

Low crop yeilds can drive up the cost of foods for consumers.

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Biology 3 Topic 1

Photoperiodic - responding to the length of days: 

A photoperiodic response is is a response to a change in the amount of light and dark in a 24 hour cycle. Some plants only germinate (sprout from a seed), grow or flower in a certain amount of light and dark.  These responses make sure they grow or reproduce at the time of year that best suits them.  

Seeds of some Artic plants only germinate if the days are very long. This makes sure they only germinate in the middle of summer, when temperatures are warm.

Some plant buds use the increasing day length to tell them that its far enough away from winter to start to grow.  This makes sure they dont sprout, only to be killed by frost.

Some plants only flower when the day is at least a certain length, to make sure they flower near summer.  Other plants only flower when the days are less than a certain length to make sure they flower in the early spring or autumn. This way, they only flower when the right insects are about to pollinate the flowers.

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Biology 3 Topic 1

Cirdcadian Rhythms: Biological process that follow a 24 hour cycle.  They include chemical patterns (eg hormone production), physiological patterns (eg body temperature) and patterns of behaviour (eg sleeping or eating). Animals, plants and microorganisms all have cirdcadian rythms. Cirdcadian rhythms are controlled internally, but they can be influenced by enviromental factors. 

Examples of Cirdcadian Rhythms in Animals include:

Sleep Patterns - The bodys master clock gets information about the light intensity from your eyes.  It uses this to control production of the hormone melatonin, which makes you sleepy.  When its dark your melatonin production increases (opposite happens to nocturnal animals).  

Uirne Productio - The bodys master clock also controls production of the hormone ADH.  At night ADH levels increase, this reduces urine production.

Examples of Cirdcadian Rhythms in Plants include: 

Stomata Opening - Stomato respond to light intensity, they open during the day and close at night.

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Biology 3 Topic 1

Examples of circadian rhythms in animals include:

  • Sleep patterns - The boyds master clock gets information about light intensity from your eyes. It uses this to control produciton of the hormone melatonin which makes you sleepy.  When it gets dark, your melatonin production increases. Having a good sleeping pattern keeps you healthy and helps you to feel awake at the right times.
  • Urine Production - The bodys master clock also controls production of ADH. At night ADH levels increase.  This reduces urine production so sleep is not interupted.

Examples of circadian rhythms in plants include:

  • Stomata opening - Stomata responds to light intensity.  They open during the day and close at night.  During the day photosynthesis occurs. The stomata opens up to let CO2 and O2 in and out.  At night, the stomata closes to reduce water loss.
  • Flower Opening - Plants can respond to light intensity by opening and closing their flowers.  They onlu need to be open when the creatures that pollinate them are active.
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Biology 3 Topic 1

LH - luteinising hormone.

  • LH surge stimulates at day 14 - the follicle ruptures and the egg is released.
  • It stimulates the remains of the follicle to develop into a structure called a corpus luteum which secretes progesterone.

Progesterone

  • Maintains the lining of the uterus.
  • Inhibits (prevents) the production of LH and FSH.
  • When the level of progesterone falls, and there is a low oestrogen level, the uterus lining breaks down.
  • A low progesterone level allows FSH to increase and then the whole cycle starts again.
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LH - luteinising hormone.

  • LH surge stimulates at day 14 - the follicle ruptures and the egg is released.
  • It stimulates the remains of the follicle to develop into a structure called a corpus luteum which secretes progesterone.

Progesterone

  • Maintains the lining of the uterus.
  • Inhibits (prevents) the production of LH and FSH.
  • When the level of progesterone falls, and there is a low oestrogen level, the uterus lining breaks down.
  • A low progesterone level allows FSH to increase and then the whole cycle starts again.
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Biology 3 Topic 1

Kidney

3 main roles of the kidney:

Removes urea from the blood.  Urea is produced in the liver from the break down of amino acids.

Adjusts levels of ions in the blood.

Adjusts levels of water content in the blood.

They do this by filtering stuff out of the blood under high pressure.

They then reabsorb the useful things.

The end product is urine.

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Biology 3 Topic 1

Ultrafilteration: High pressure is built up which squeezes water, urea, ions and glucose out of the blood and into the Bowmans Capsule.The glomerulus and the Bowmans Capsule act like filters. Big molecules like proteins and blood cells are not squeezed out and stay in the blood.

Reabsorption:  When the liquid flows along the nephron, useful substances are reabsorbed. All the glucose is selectively reabsorbed, its moved out of the nephron and back into the blood against the concentration gradient. Sufficient water is reabsorbed according to the level of ADH. The process of maintaining the correct water content is osmoregulation.

Disposal of Wastes: Urea and excess water are not reabsorbed. They continue out of the nephron into the ureter and down the bladder as urine.  Urine is released through the uretha.

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Biology 3 Topic 1

Removing waste products (http://www.bbc.co.uk/staticarchive/88747e79a5e052b9b3f4e4ef612824a1279d1f47.gif)

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Biology 3 Topic 1

Sexual Reproduction:

Main function of EGG: carry female DNA and nourish the developing embryo in early stages.

Main function of SPERM: transport male DNA to females egg so their DNA can combine.

EGG: contains nutrients in the cytoplasm to feed the embryo. Straight after fertilisation the egg membrane changes its structure to stop any more sperm getting in. This makes sure the offspring ends up with the correct amount of DNA.  The egg contains a haploid nucleus so when the egg is fertilised, the resulting cell will have the right number of chromosomes.

SPERM: small and have long tails so they can swim to the egg.  They have lots of mitrochondria in their middle section to provide the energy from respiration needed to swim this distance.  They have acrosome at the front of their head where they store the enzymes they need to digest their way through the membrane of the egg cell. Sperm contains a haploid nucleus, meaning they have only one copy of each chromosome.

Gamete - for a female its an egg, for a male its the sperm. When the gametes join they form a zygote. Human sperm and egg cells contain 23 chromosomes, a zygote contains 46.

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Biology 3 Topic 1

Menstrual Cycle:

Stage 1: Day 1 is when the bleeding starts.  The uterus lining breaks down and is released (menstruation).

Stage 2: The lining of the uterus breaks down again, from day 4 to day 14, into a thick, spongy layer of blood vessels, ready to recieive the fertilised egg.

Stage 3: Aan egg is released from the ovary (ovalation) at about day 14.

Stage 4: The lining is then maintained for about 14 days, until day 28. If no fertilised egg has landed on the uterus wall by day 28, the spongy lining breaks down again and the whole cycle repeats.

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