Sensitivity

Sensitivity:
Sense organs detect changes inside and outside your body. Scientists used to think humans had 5 senses but now we know we have many more including heat, cold, pain and changes in position. A stimulus are change in a environmental factor that is detected by receptors. Sense organs contain receptor cells which detect a stimulus.

Receptor cells create electrical signals which are called impulses, they usually travel to the brain. The brain processes this information and sends impulses to other organs to alter the way the body works.

Electrical impulses travel along cells called neurones. The travelling of impulses are called neurotransmission. There are many dendrons in a neurone which have many branches at the end of it called dendrites. The dendrites receive impulses from receptor cells. The impulse moves along the dendron to the axon. It then goes to the ending where it passes on to other neurones.

Neurones are all packed together to create nerves. The spinal cord is connected to the brain and contains many packed together nerves. The brain and spinal cord together form The Central Nervous System. This controls your body.


Key Words:

Sense organs
Stimulus
Receptor cells
Impulses
Neurones
Neurotransmission
Dendrons
Dendrites
Axon
Nerves
Spinal cord
Central Nervous System


Questions:

1. What is a stimulus?
2. State one way in which the brain alters the way the body works to stop it getting too cold.
3. Why is it necessary for neurones to link to each other?
4. Which organs are in the CNS?
5. When you pick up an ice cube how does your brain know it's an ice cube?


What you should've learnt:

That the Central Nervous System consists of the brain and spinal cord and is linked to sense organs by nerves.

The structure and function of dendrons and axons in the nervous system.

How stimulation of receptors in the sense organs send electrical impulses along neurones.

Homeostasis

Homeostasis:

The internal environment of the body must remain stable. It needs enough water for substances to dissolve and for chemical reactions to take place inside the cells. But too much water can cause swellings and high blood pressure. Keeping the internal environment of the body stable is called homeostasis.

The body loses water when we breathe and sweat. Sweat is produced by sweat glands in the skin. It can also lose water in urine so if the body contains too much water the kidneys produce more urine. If the body has little water the kidney produces little water and the brain responds by making you feel thirsty. The control of water in the body is called osmoregulation. The control of glucose in the blood is blood glucose regulation. 

The body's temperature is 37C. The control of body temperature is Thermoregulation.

Hypothalamus is part of the brain that constantly monitors temperature. It receives information from nerve endings in the dermis of the skin about temperature outside of the body. If body temperature goes below 37C hypothalamus causes muscles to shiver. It releases heat which warms you up.

Hypothalamus also causes erector muscles in the dermis to contract. It causes body hairs to stand upright. Oils released from sebaceous glands at the base of the hair keep the skin lubricated and in good condition. It also reduces blood flow near the skin.

If body temperature goes above 37C hypothalamus causes us to sweat. When sweat evaporates it transfer heat energy from the skin to the surroundings so the skin cools down. Hypothalamus also increases blood flow near the skin so we look pinker.

When it's cold hypothalamus reduces blood flow by narrowing blood vessels. This is called vasoconstriction. Vasodilation (when blood vessels widen) happens when the body needs to lose heat.

The control of body temperature is an example of negative feedback. This means as a change to the body happens in one direction mechanisms in the body work to make it change in the opposite direction. This helps conditions in the body stay under control.


Key Words:

Internal environment
Homeostasis
Sweat glands
Urine
Kidneys
Osmoregulation
Blood glucose regulation
Thermoregulation
Hypothalamus
Dermis
Erector Muscles
Sebaceous glands
Vasoconstriction
Vasodilation
Negative feedback


Questions:

1. What is Homeostasis?
2. What is getting thirsty a sign of?
3.  Why do people shiver when it's cold?
4. What is vasocontriction and vasodilation?
5. What changes would happen to your body if you spent 1hr in a greenhouse? Why?


What you should've learnt:

Homeostasis as the maintenance of a stable internal environment.

An understanding of the homeostatic mechanisms of: a. thermoregulation and the effect of temperature on enzymes  b. Osmoregulation  c. Blood glucose regulation. 

How thermoregulation takes place, with reference to the function of the skin , including: a. the role of the dermis-sweat glands, blood vessels, nerve endings, hair, erector muscles and sebaceous glands  b. the role of the hypothalamus-regulating body temperature.

How thermoregulation takes place, with reference to: a, vasoconstriction  b. vasodilation  c. Ngeative feedback.

Genetic Disorders

Genetic Disorders:

Sickle cell disease is a genetic disorder caused by faulty alleles. The Sickle cell allele is recessive so only people with two copies of the allele suffer from the disorder.

People with the disease easily become tired and short of breath. Their joints can become very painful because their red blood cells stick together and block blood vessels. This can sometimes be fatal.

Another genetic disorder also caused by a recessive allele is cystic fibrosis. People with the disorder have their lungs clogged with thick mucus making breathing difficult which leads to infections. It also blocks tubes that carry enzymes to the small intestine. This can result in weight loss.

A family pedigree chart shows which members of a family suffer from a disorder. It allows you to see how a genetic disorder is passed on in a family.

Doctors use pedigree charts to work out the probability that a person may have inherited the disorder from their parents. This is called Pedigree analysis.


Key Words:

Sickle cell disease
Genetic disorder
Cystic Fibrosis
Family pedigree chart
Pedigree analysis


Questions:

1. State two symptoms of Sickle cell disease?
2. State two symptoms of Cystic fibrosis?
3. Why can't people catch sickle cell disease like catching a cold?
4. Why might Cystic Fibrosis sufferers lose weight?
5. Cystic fibrosis is a recessive genetic disorder. Explain what this means.


What you should've learnt:

How to analyse and interpret patterns of monohybrid inheritance using a genetic diagram and family pedigrees.

The symptoms of the genetic disorders: a. Sickle Cell Disease   b. Cystic Fibrosis

The outcomes of pedigree analysis when screening for genetic disorders a. Sickle Cell Disease  B. Cystic Fibrosis.

Explaining Inheritance

Explaining Inheritance:

Plants and animals produce gametes (sex cells) The male produce sperm cells in animals and pollen grains in plants. The female gametes are egg cells in plants AND animals. Gametes have only one copy of each chromosome.

Gametes have only one allele for each gene. In sexual reproduction the gametes fuse together, so the new organism formed contains two alleles for each gene. (one from each parent).

If the offspring receives two alleles for flower colour from it's parents. (one being white and one purple) only the allele for purple flowers would have an effect because it's said to be dominant. The white flower allele has no effect and is described as recessive.

A recessive characteristic is only seen if both alleles are recessive, this can be shown in a genetic cross diagram. This shows possible combinations of alleles when two organisms breed.

Dominant alleles are shown by a capital letter and recessive the same letter but in lower case. The alleles in an organism are it's Genotype. What the organism looks like it it's Phenotype.

Homozygous are if both alleles for a characteristic are the same.
Heterozygous are if both alleles for a characteristic are different.

Possible genotypes produced can be shown in a Punnet Square. 
It's a diagram used to predict different characteristics that will be present in the offspring of two organisms with known combinations of alleles. Using the square you can work out the probability that the offspring will inherit a certain feature.


Key Words:

Gametes
Sperm Cells
Pollen Grains
Egg Cells
Dominant
Recessive
Genetic cross diagram
Genotype
Phenotype
Homozygous
Heterozygous
Punnet Square
Probability


Questions:

1. How many chromosomes are in a normal human sperm cell?
2. When will a recessive allele affect a phenotype?
3. The pea plant gene for height has two alleles T (dominant, causing tall plants) and t (recessive, causing short plants) Draw a punnet square showing this.
4. What's the percentage probability of getting a tall phenotype plant?


What you should've learnt:

The meaning of, and use appropriately, the terms: dominant, recessive, homozygous, heterozygous, phenotype and genotype.

How to analyse and interpret patterns of monohybrid inheritance using a genetic diagram and Punnet squares.

How to calculate and analyse outcomes (using probabilities, ratios and percentages) for monohybrid crosses.

Genes

Genes:

Three of the main parts of the cells are the cell membrane, Cytoplasm and the Nucleus. In the nucleus there are long strands of a substance called DNA. Each strand forms chromosome.

The nucleus contains different chromosomes and there are usually two copies of each type of chromosome.

Chromosomes are divided into genes. With each chromosome carrying a large number of genes and each gene doing a particular job. Variation caused by genes is inherited variation as we inherit our genes from our parents.

To make it easier to think of chromosomes you should think of it as a set of books. Each book (chromosome) contains a set of sentences giving instructions (genes). All of the books together contain all of the instructions needed to produce a certain organism.

Alleles- Every gene comes in different types called alleles. So a gene for eye colour may come in a 'blue type' allele and a 'brown type' allele. Alleles are different forms of the same gene.

There are two copies of every chromosome in a nucleus so there are two copies of each gene. Every copy of a gene must be a different allele.

Different organisms have a different number of chromosomes. Humans have 23 pairs with 23 000 genes in total. Each different set of alleles that we inherit from our parents give each of us slightly different characteristics.


Key Words:

Cell membrane
Nucleus
Cytoplasm
DNA
Chromosome
Genes
Inherited Variation
Alleles


Questions:

1. Which part of the cells are chromosomes found?
2. Where are genes found?
3. What are alleles?
4. How does alleles explain the idea that we all look different?
5. Using you knowledge of science and genes how do you think a scientist would find out whether blood at a crime scene belongs to the victim or a suspect?


What you should've learnt:

The structure of the nucleus of the cell as containing chromosomes, on which genes are located.

An understanding that genes exist in alternative forms called alleles which give rise to differences in inherited characteristics.

Evolution

Evolution:

Organisms produce more offspring then the environment can support. Most will die before reaching adulthood because of the simple fact being there aren't enough resources for them all.

Offspring will show variation in their characteristics but some variations will be better adapted to the environment then others. Limited resources will cause competition between individuals. Those who are better suited to the environment are more likely to survive while others will die. This is called 'Survival of the Fittest' or Natural Selection. They'll pass on their variations to their offspring.

Evolution means a gradual change over time. Charles Darwin (1809-1882) drew together several ideas to produce a theory. 
He knew there was competition between individuals. Darwin realised that if the environment changed different variations may be better suited to the new conditions. So the range of variation in characteristics of the population will gradually change over generations, called evolution.
If the environment changes too quickly and organisms don't have adaptations to help them survive, they'll die out and their species may become extinct.


A problem for Darwin's theory was that there was little evidence for it as Evolution takes time to observe.

Warfarin is a chemical that was used to poison rats. When it was first used most rats that ate it died. Within 10 years rats were resistant to warfarin.
Because of Variation there were always some rats that were resistant but no one realised this. So when the poison killed the non-resistant rats the only ones left to breed were resistant.


Speciation is a formation of new species, such as when populations of a species are separated geographically and evolve until they are no longer capable of interbreeding.



Key Words:

Competition
Survival of the Fittest
Natural Selection
Evolution
Extinct
Resistant
Speciation


Questions:

1. Why is there competition between individuals?
2. What is meant by 'Survival of the Fittest'?
3. How can a species become extinct?
4. How did rats become resistant to warfarin?
5. Ground finches have large, powerful beaks to crush seeds. A closely related species has a narrow beak for probing in small holes for insect larvae. Suggest
how this species could've evolved from the seed-eating species.


What you should've learnt:

An understanding of Darwin's theory by Natural Selection including a. Variation  b. over-production  c. Struggle for existence  d. Survival  e. advantageous
characteristics inherited  f. gradual change.

An understanding of how speciation occurs as a result of geographic isolation.

How new evidence from DNA research and the emergence of resistant organisms support Darwin's theory.

Reasons for Variety

Reasons for Variety:

Organisms are all adapted to their surroundings. This means that they have variations in their characteristics that allow them to survive in their habitats.

Organisms that come from polar region (e.g. the polar bear) are adapted to the cold. Organisms living near deep-sea hydrothermal vents are adapted to hot temperatures. Organisms living there cope with big temperature changes, complete darkness and huge pressures.


How the Polar Bear is adapted:

• Small ears to stop it losing heat
• Thick fur for insulation
• White fur for camouflage
• thick layer of blubber under the skin for insulation
• Large feet to spread it's weight and stop it sinking in the snow.
• Rough soles to grip the ice.

How Deep-sea Pompeii worms are adapted:

• It's body adapted to pressures over 200 times those at sea level
• It spends its time in a papery tube to protect it from predetors
• No eyes but very sensitive tentacles.
• The worms body is covered in a layer of bacteria to help protect it from the heat. (copes with temp changes from 40C-90C

Discontinuous variation is normally caused by instructions within your cells and is called genetic variation.

If a characteristic shows continuous variation and we take data from a large number of people we often get a graph with a particular shape.
This is called a Normal Distribution Curve. This shows that most individuals measure within the middle part of the range in variation, with  fewer individuals at the extremes of the range.

Characteristics that show continuous variation are normally controlled by both genes and the environment. You may inherit shortness from your parents. This is called Inherited Variation. But, if you don't eat healthily or have an accident that damages your bones you may never grow tall.
Shortness will have been an acquired characteristic which is caused by the environment. This is called Environmental Variation.


Key Words:

Adapted
Habitats
Hydrothermal Vents
Genetic Variation
Normal Distribution Curve
Acquired Characteristic
Environmental Variation


Questions:

1. Which from the polar bears adaptations help it to survive in its habitat?
2. Why doesn't the pompeii worm need eyes?
3. Why is 'gender' an example of discontinuous variation?
4. What is a normal distribution curve?
5. Is human height inherited or acquired? Explain your answer?


What you should've learnt?


How organisms are adapted to their environment and how some organisms have charcateristics that enable them to survive in extreme environments.

How to interpret information of variation using normal distribution curves

Demonstrate an understanding on the causes of variation , including:
a. genetic variation - different characteristics as a result of mutation or reproduction. b. Environmental variation - different characteristics
caused by an organism's environment.

Variation: PCA

Variation: PCA:


When measuring variation in certain characteristics there are a range of values with some values more common then others. E.g. Human
adult height ranges from 87cm-246.5cm BUT most are 150-190cm.

Range in human height is caused by both inherited and environmental variation. This is an example of continuous variation. This means the values can be any number within a certain range.

Shoe size is Discontinuous variation. Which means they only have a fixed set of values.


Key Words:

Continuous Variation
Discontinuous Variation


What you should've learnt:


Variation as continuous and discontinuous.

Investigate variations within a species to illustrate continuous variation and discontinuous variation.

Variation

Variation:

Differences in characteristics are called Variation. There is variation within a species but more variation within different species. Variation within  a species can make classification difficult.

So that scientists know that a new organism isn't just a hybrid they find more then one of the organism.

To identify new species you can use a key. A key is a diagram containing a set of questions/statements that is used to work out an organisms name.

Classification using the Binomial System allows biologists to:
Identify existing and new species easily.
See relations between organisms.
Identify the areas of greater or lesser biodiversity.

Biodiversity is a variety of species of plants and animals. It's measuring the amount of different species that live in a particular area.

Biodiversity is important because we receive many products from living things. So the more species the more choices we have for now AND the future.
Plus biodiverse areas are better at recovering from natural disasters.

Biodiversity hotspots (areas of greater biodiversity) are places biologists think need most time and money spent on trying to conserve them as it will result in a greater number of species being conserved.

Key Words:

Variation
Key
Biodiversity
Biodiversity Hotspots


Questions:

1. What is variation?
2. How does classification make it easier to measure biodiversity?
3. Why is it important to protect biodiversity hotspots?
4. Why do scientists need to find more then one example of a new organism?
5. Design a key to identify some farm animals. Try and include animals from the same AND different species.


What you should've learnt:


Why Binomial Classification is needed to identify, study and conserve species, and can be used to target conservation efforts.

How accurate Classification may be complicated by a. variation within a species.

Construct and use keys to show how species can be identified.

Species

Species:

A Species is a group of organisms that can interbreed (reproduce with one another) to produce offspring that are fertile (able to reproduce).

But sometimes two closely related species can breed and produce Hybrids. Hybrids aren't one species nor the other which show characteristics from both parents. Hybrids are usually infertile (unlikely to have offspring of their own).

Neighboroughing populations of the same species may have slightly different characteristics but still interbreed. Sometimes there's a chain of different populations that can all breed with their neighboroughing population BUT the two populations at either end of the chain
can NOT interbreed. These organisms are called ring species.

An organism's scientific name has two latin words, the Genus and Species. This is called the Binomial System. Organisms that share the first word in their name are closely related.
Binomial System is also useful because those with the same common names may actually be a different species. E.g. The robin in America isn't the same species as a robin in the UK.
The system is a way of scientists around the world to be able to communicate.


Key Words:

Species
Interbreed
Fertile
Hybrids
Ring Species
Binomial System


Define these in your revision notes.


Questions:

1. Why can't American and British Robins interbreed?
2. What is a Hybrid?
3. Why's it hard to divide populations that form ring species into separate species?
4. Why is the Binomial System useful?
5. Why is it difficult to define what we mean by the term 'species'?


What you Should've learnt:

Why the definition of a species as organisms that produce fertile offspring may have limitations; some organisms don't always reproduce sexually
and some hybrids are fertile.

Why Binomial Classification is needed to identify and study species.

Explain how accurate classification may be complicated by: b. Hybridisation in ducks c. Ring species.

The role of the scientific community in validating new evidence, including the use of: a. Scientific journals b. the peer review process c. Scientific
conferences.

Vertebrates and Invertebrates

Vertebrates and Invertebrates:

When the Platypus was discovered scientists weren't sure as to which group they should classify it into. The platypus was 
a poisonous furry animal with a duck's beak, beavers tail, otter's feet, lizard's skeleton shape and layed leathery eggs.
Scientists did agree that it was a vertebrate (Animals that have a backbone).
All vertebrates belong to the Phylum Chordata because they have a supporting rod which runs the length of their body.

Animals with no backbone are called invertebrates. Vertebrates and Invertebrates are divided into smaller groups.

The five vertebrate groups are:

Fish- Gills, Fins, Wet scales, External Fertilisation
Amphibian- Smooth skin, lungs/gills, External Fertilisation
Reptile- Dry scaly skin, Eggs with hard shells, Internal Fertilisation
Bird- Wings, Feathers, Eggs with hard shells, Internal Fertilisation
Mammal- Hair/fur on body, give birth to live young, feed young on milk, Internal Fertiliastion

External Fertilisation is when a female releases her eggs in the water where they're fertilised by adult male sperm
Internal Fertilisation is when sperm is placed inside the female so fertilisation takes place inside her body.

If an animal lays eggs it's oviparous.
If an animal gives birth to live young it's viviparous.

Some vertebrates are homeotherms which means they keep their body temperature constant and often warmer then their surroundings
by releasing heat from reactions in their body.

Some vertebrates are poikilotherms which means that their body temperature varies with the temperature of their surroundings.


Key Words:

Vertebrates
Chordata
Invertebrates
Fish
Amphibian
Reptile
Bird
Mammal
External Fertilisation
Internal Fertilisation
Oviparous
Viviparous
Homeotherms
Poikilotherms


Questions:

1. What is a backbone and what is it's purpose?
2. Why is the Platypus a Chordata?
3. How are reptiles and birds similar? How are they different?
4. What characteristic separates birds and mammals from other vertebrates?
5. Why was it difficult to classify the Platypus?


What you should've learnt:

Describe the main characterisitcs of the phylum chordata as animals with a supporting rod running the length of the body, an
example of this being the backbone in vertebrates.

Explain how scientists place vertetbrates into groups based on a. Oxygen absorpsion methods - lungs, gills and skin
b. Reproduction - internal or external fertilisation, oviparous or viviparous c. thermoregulation - homeotherms and
poikilotherms.

Demonstrate an understanding of the problems associated with assigning vertebrates to a specific group based on their
anatomy and reproduction methods and why many vertebrates are difficult to classify.

Classification

Classification:

Sea sponges used to be thought of as plants. This was due to Aristotle who sorted organisms into groups based on
their characteristics. This was called Classification. Aristotle thought any organism that didn't move was a plant.

Organisms with many characterisitics in common are all together grouped as a species. Species that share many
characteristics are together grouped as a genus. Genus that share many characteristics are together grouped as
a family. And so on untill Kingdom is reached.

The order is:
Kingdom      Phylum       Class      Order     Family       Genus        Species

To help remember them use:
Keep         Plates       Clean      Or        Family       Gets         Sick


Organisms can be classified into one of five Kingdoms according to some characteristics. Some organisms are unicellular
(Single cells) others are multicellular (Made of many cells). Many organisms have cells that contain a nucleus. But bacteria doesn't have a nucleus.

Another characteristic is how an organism gets its food.

Plants make their food autotrophically using Photosynthesis- Making food from molecules using a energy source.
Animals feed heterotrophically- Getting food by eating a digesting other organisms.
Fungi feed saprophytically- Digesting organisms outside the body and absorbing the digested food.


Kingdom:                        Main characteristics:
Animalia                        Multicellular; heterotrophic feeders so no chlorophyll; no cell walls; complex cell
                                structure with nucleus.

Plantae:                        Multicellular; autotrophic feeders using chlorophyll; cell walls made of cellulose;
                                complex cell structure with nucleus.

Fungi:                          Multicellular; cell walls not made of cellulose; saprophytic feeders so no chlorophyll;
                                complex cell structure with nucleus.

Protoctista:                    Mostly unicellular; complex cell structure with nucleus.

Prokaryotae:                    Unicellular; simple cell structure with no nucleus.



Remember: There is no Kingdom for Viruses because most scientists don't think of them as being alive. This is because they don't
show all seven life processes and had to live inside a living cell.


Key words to remember: 

• Characteristics
• Classification
• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species
• Multicellular
• Unicellular
• Nuclus
• Bacteria
• Autotrophically
• Photosynthesis
• Heterotrophically
• Saprophytically
• Animalia
• Plantae
• Fungi
• Protctista
• Prokaryotae
• Virus

Define these words in your revision notes.

Questions:

1. Why did Aristotle think sponges were plants?
2. What is Classification?
3. Seaweeds don't have cellulose cell walls but do photosynthesise. Suggest why seaweeds were thought of as plants?
4. Why do you think seaweed is no longer classified as plants?
5. Viruses don't have a nucleus but nor do bacteria. Why are viruses not classified as Prokaryotae with bacteria?


What you should've learnt:

Demonstrate an understanding of how biologists classify organisms according to how closely they're related to one another including
a. Species  b. Genus  c. Family  d. Order  e. Class  f. Phylum  g. The Five Kingdoms

Describe the main characteristics of the five kingdoms including a. Animalia b. Plantae c. Fungi d. Protoctista e. Prokaryotae

Explain why scientists don't classify viruses in any of the Five Kingdoms and regard them as non-living.

Welcome!

Hi
I'm having a Biology exam on November 5th 2012 and have dedicated this blog purely for all my revision and for anyone who needs revision resources.
I'll write all of my revision notes on it so it's easier for us all to revise.
Please spread the word about this if you can and know anyone taking this exam.
Thanks

Shakira x