Biology Paper 2 Flashcards
Homeostasis
Maintainence of a constant internal environment
Conditions maintained by homeostasis in our body
-blood glucose concentration
-body temperature
-water levels.
Components all control systems have
-receptors, which detect stimuli (changes in the environment)
-coordination centres (such as the brain, spinal cord and pancreas) that receive and process information
-effectors, muscles or glands, Cary out response
2 types of responses that are used in control systems
Nervous
Chemical
Order
Receptor cells
Sensory neurons
Relay neurons
Motor neuron
Effectors
How do nervous systems work?
stimulus —> receptor —> coordinator —> effector —> response
Nervous system
Respond to stimuli
The CNS is the brain and spinal cord.
Reflex actions
are automatic and rapid response; they do not involve the conscious part of the brain.
Describe reflex arc
The stimulus is detected by the receptor
An electrical impulse passes sensory neuron to CNS.
At a synapse between two neurons, a neurotransmitter diffuses through the gap .
First with sensory and relay neuron then with relay and motor neurone.
After at the effector, a response is carried out.
Endocrine system
Collection of glands that produce hormones.
Hormones
Chemical messengers that help regulate processes in the body.
Pancreas
(middle of body)
Produces insulin and glucagon. Responsible for controlling blood glucose levels.
Thyroid gland
(neck)
Produces thyroxine, controls metabolic rate.
Important for growth and development.
Adreum gland
(left side of pancreas)
Produces adrenaline, prepares body for fight/flight, increases the heart rate.
Boosts the delivery of oxygen
and glucose to the brain and muscles.
Ovaries
(below adreum)
Produces oestrogen, coordinates menstrual cycle
Testes
Produces testosterone, coordinates production of sperm
Insulin
If glucose levels are too high, insulin is produced, excess blood glucose is converted into glycogen in liver and muscle cells.
Glucose is lowered
Glucagon
If glucose levels are too low, causes glycogen to convert back to glucose
Glucose is raised.
Glucagon
Converts glycogen to glucose
Glycogen
Storage sugar in animals
Neurotransmitter
Chemical that crosses the synapse
Type 1 diabetes
Pancreas fails to produce insulin. Treated with insulin injections
Type 2 diabetes
Body cells no longer respond to insulin.
Prevented by carbohydrate controlled diet, exercise
Follicle stimulating hormone
Produced in pituitary glands
Causes an egg to mature.
Luteinising hormone
Produced in pituitary glands.
Stimulates release of a mature egg
Oestrogen
Made by ovaries. Inhibits FSH and stimulates LH, causes uterus lining to thicken
Progesterone
Produced in ovaries. Inhibits FSH and stimulates LH, maintains thick uterus lining.
Preventing pregnancy
-Contraceptive pill
Inhibits FSH, eggs don’t mature
Progesterone produces thick mucus, preventing sperm cell reaching an egg.
-Contraceptive skin patch
Oestrogen and progesterone prevents release of an egg
-Contraceptive implant
Lasts for 3 years, inserted under skin.
Prevents release of an egg
-Contraceptive injection
Contains progesterone, lasts for 3 months.
Prevents release of an egg, produces mucus
-Intrauterine device
Plastic device inserted to uterus
Releases progesterone which produces mucus, prevents spermicide reaching the egg
Other methods…
-Barrier methods such as condoms and diaphragms which prevent the sperm reaching an egg
-Spermicidal agents which kill or disable sperm
-Abstaining from intercourse when an egg may be in the
oviduct
-Surgical methods of male and female sterilisation.
Ovulation
Release of mature egg from ovaries.
In Vitro Fertilisation (IVF) treatment.
- IVF involves giving a mother FSH and LH to stimulate the maturation of several eggs.
- The eggs are collected from the mother and fertilised by sperm from the father in the laboratory.
- The fertilised eggs develop into embryos.
- At the stage when they are tiny balls of cells, one or two embryos are inserted into the mother’s uterus (womb).
Advantages and disadvantages of IVF
Advantages- Can store eggs for later. Infertile couples can have children.
Disadvantages- It is very emotionally and physically stressful, the success rates are not high, lead to multiple births, risk to mother and baby
Negative feedback
-Type of control where body responds to an increase/ decrease in a factor by returning it to optimum level.
-Thyroxine levels are controlled by negative feedback.
Sexual reproduction
2 parents needed.
Joining (fusion) of male and female
gametes
Each parent produces sex cells called gametes.
Meiosis
Advantages and disadvantages of sexual reproduction
Advantages - wide diversity, survival as people are unique so disease can’t spread easily, organisms can adapt.
Disadvantage- 2 parents needed, takes longer and require more energy, so less offspring produced.
Asexual reproduction
Requires 1 parent.
No fusion of gametes. There is no mixing of genetic information.
This leads to genetically identical offspring (clones).
Mitosis
Advantages and disadvantages of asexual reproduction
Advantages - population can increase a lot, faster, only 1 parent needed, safer (less change of mutation)
Disadvantage- disease may affect all people, overpopulation, lack of diversity, as all offspring are identical, cannot adapt.
Meiosis
Produces haploid cells
Produces cells with 23 chromosomes
Produces genetically different cells
2 cell divison
Produces 4 daughter cells
Sexual
Meisosis (2)
Meiosis halves the number
of chromosomes in gametes and fertilisation restores the full number of chromosomes.
The new cell divides by mitosis. The number of cells Increases. As the embryo develops cells differentiate.
Cells in reproductive organs divide by meiosis to form gametes.
When a cell divides to form gametes:
* copies of the genetic information are made
* the cell divides twice to form four gametes, each with a single
set of chromosomes
* all gametes are genetically different from each other.
Mitosis
Produces diploid cells
Produces cells with 46 chromosomes
Produces genetically identical cells
One cell divison
Produces 2 daughter cells
Asexual
DNA
The genetic material in the nucleus of a cell is composed of a chemical called DNA.
DNA is a polymer made up of two strands
forming a double helix.
The DNA is contained in structures called
chromosomes.
Gene
A small section of DNA on a chromosome.
Each gene codes for a particular sequence of amino acids, to make a specific protein.
Genome
all genetic material of an organism
Gametes
sex cells in egg cells
Chromosomes
Long strands of DNA coiled up together
Mutation
A mutation is a permanent change in the nucleotide sequence of DNA.
A mutation may change the structure or shape of a protein.
Alleles
Different versions of a gene
People’s characteristics are determined by the alleles that they have
Dominant allele
Only 1 needs to be present on the chromosomes for its characteristics to be expressed.
eg only B needs to be present
We represent the dominant green allele with an
uppercase letter, and the recessive yellow allele with
lowercase letters on a Punnett square.
Hetrozygons
2 alleles for a gene that are different.
Recessive allele
2 of these need to be present on the chromosomes for the characteristic to be expressed.
A recessive allele is only expressed if the other allele is
recessive.
Eg bb
Homozygous
2 alleles for a gene that are the same.
Genotype
combination of alleles an organism has
Phenotype
characteristic the organism has.
Phenotype is determined by the interaction between genotype and environment
Why is understanding the human genome important?
-Search for genes linked to different types of disease
-Understanding and treatment of inherited disorders
-Use in tracing human migration patterns from the past.
In 2003, the Human Genome Project was completed. Researchers had successfully studied the entire human genome.
Sexual reproduction involves the joining (fusion) of male and female
gametes:
- sperm and egg cells in animals
- pollen and egg cells in flowering plants.
Polydactyly (having extra fingers or toes)
is caused by a dominant allele.
With one suffering parent (heterozygote), and one non-suffering parent (homozygote recessive), 50% of the offspring will have extra toes or fingers.
Cystic fibrosis (a disorder of cell membranes)
is caused by a recessive allele.
inherited disease
causes thick, sticky mucus to build up in lungs and digestive system
Embryo screening
Procedure were people can find out whether they have any problems with the chromosomes in the embryo
Advantages and Disadvantages of embryo screening
Advantages- Lets parent know if child is inherited, help people not suffer, would ensure that the implanted embryos are healthy, save money as reduction is disorders.
Disadvantages- very expensive, Screening is not 100 % accurate, ethical, discrimination
Sex determination
22 pairs control characteristics only, but one of the pairs carries the genes that determine sex.
- Females- chromosomes are the same (XX).
- Males- the chromosomes are different (XY).
Variation
Differences in the characteristics of individuals in a population is called variation
Differences in the characteristics of individuals in a population is called variation and may be due to differences in:
- The genes they have inherited (genetic causes)
- The conditions in which they have developed (environmental causes)
- A combination of genes and the environment
Mutation
Any change in the DNA sequence of a cell.
Mutations occur continuously.
Very rarely a mutation will lead to a
new phenotype.
If the new phenotype is suited to an environmental change it can lead to a relatively rapid change in the species
Speciation
Development of new species, as phenotype changed so much.
Evolution
Change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species.
The theory of evolution by natural selection states that all species of
living things have evolved from simple life forms that first developed
more than three billion years ago.
Organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success.
Selective breeding
Selective breeding happens when humans choose animals and crops to reproduce, based on their genetic characteristics.
The characteristic can be chosen for usefulness or appearance:
- Disease resistance in food crops.
- Animals which produce more meat or milk.
- Domestic dogs with a gentle nature.
- Large or unusual flowers.
Potential problems caused by selective breeding include:
Inbreeding- prone to disease
reduced variation within a population
Organisms that have been selectively bred for their useful characteristics include:
Crops
Disease resistance
Farm animals
Produce more meat or dairy to increase yield
Flowers
Visual features, such as colour and size
Dogs
Docile-nature
Process of selective breeding
Choose parents who most strongly display the desired characteristic and produce offspring
From the resultant offspring, choose the ones that best display the desired characteristic and breed these offspring
Repeat this process of breeding and re-selection over many generations
Genetic engineering
Genetic engineering involves modifying (changing) an organism’s genome by introducing a gene from another organism to produce a desired characteristic.
Plant crops have been genetically engineered to be resistant to diseases or to produce bigger better fruits.
What is the process of genetic engineering?
- Enzymes are used to isolate the required gene; this gene is inserted into a vector, usually a bacterial plasmid or a virus
- The vector is used to insert the gene into the required cells
- Genes are transferred to the cells of animals, plants or microorganisms at an early stage in their development so that they develop with desired characteristics.
Uses of genetic engineering
Plant crops have been genetically engineered to be resistant to diseases or to produce bigger better fruits.
Bacterial cells have been genetically engineered to produce useful
substances such as human insulin to treat diabetes.
Advantages and disadvantages of genetic engineering
Advantages of genetic engineering
Preventing inherited diseases.
Improving food production efficiency.
Disadvantages about genetic engineering
Because it is a relatively recent development, it is uncertain what the long-term effects may be.
Some consider it unethical to create new life forms or move genes between species.
Reduce biodiversity.
Advantages and disadvantages of GM crops
Advantages of genetically modified (GM) crops
GM crops generally show increased yields.
They could help to provide the nutrients that are often missing from the diets of those living in developing nations.
For example, golden rice can help reduce vitamin A deficiency, which can cause blindness.
Disadvantages of genetically modified (GM) crops
The effect on populations of wild
flowers and insects.
Some people feel the effects of eating GM
crops on human health have not been fully explored.
The two main sources of evidence for evolution are:
Antibiotic resistant bacteria
Bacteria reproduce rapidly.
Mutations occur during reproduction.
If a mutated bacterium is resistant to antibiotics, it will survive exposure to antibiotics and go on to reproduce.
This bacterium will represent the original ancestor of a new resistant strain.
Fossils
Fossils are the ‘remains’ of organisms from millions of years ago, which are found in rocks.
Extinction
Extinctions occur when there are no remaining individuals of a species still alive.
Environmental changes too quickly
New predator kills them (overhunting)
Disease
Cant compete for food
Resistant bacteria
- Superbug is the name given to a strain of bacteria that is antibiotic resistant.
*MRSA is so dangerous because it is resistant to most antibiotics
Bacteria can evolve rapidly because they reproduce at a fast rate.
Mutations of bacterial pathogens produce new strains. Some strains might be resistant to antibiotics, and so are not killed.
They survive and reproduce, so the population of the resistant strain rises.
The resistant strain will then spread because people are not immune to it and there is no effective treatment.
Thermoregulation
Thermoregulation is maintenance of a constant internal temperature.
Example of natural selection
Mutations of bacterial pathogens produce new strains.
Some new strains of bacteria might become resistant to certain antibiotics, such as penicillin and cannot be destroyed by the antibiotic.
They survive and reproduce, so the population of the resistant strain rises.
The resistant strain will then spread because people are not immune to it and there is no effective treatment.
The evolution of the bacteria is an example of natural selection.
Development
- The development of new antibiotics has had some limited success however the development of new antibiotics is slow and costly.
- People are concerned that the slow development of new antibiotics for new resistant strains of bacteria means that in the near future, some bacteria will be resistant to all known antibiotics.
*The development of new antibiotics is costly and slow. It is unlikely to keep up with the emergence of new resistant strains.
MRSA is resistant to antibiotics.
- doctors should not prescribe antibiotics inappropriately, such as treating non-serious or viral infections
- patients should complete their course of antibiotics so all bacteria are killed and none survive to mutate and form resistant strains
- the agricultural use of antibiotics should be restricted.
*Previously, antibiotics were regularly used in farming, and these can be used to prevent disease, keep the animals well and allow them to grow quickly. The high use of antibiotics in agriculture may have a cost as it could lead to spread of antibiotic resistance from animals into human hosts. Legal controls are now in place to try and reduce the use of antibiotics in this way.
- High hospital hygiene levels, including regular hand washing by staff and visitors.
- Patients who are infected with antibiotic resistant strains of bacteria should be isolated from other patients.
Fossils are the remains or traces of ancient life.
Fossils are found in rocks and have been preserved by natural processes. There are 3 different ways of forming fossils:
Mineral replacement
Hard parts of organisms are gradually replaced by minerals as they decay slowly, creating a rock-like substance.
Preservation when decay is not possible
Where decomposers cannot act, preservation is possible.
Decomposers cannot operate in glaciers (extreme, low temperatures) or no oxygen presented
Hardening soft materials
The hardening of soft materials can produce casts or impressions, such as footprints.
Why is the fossil record incomplete?
A lot of early life forms were soft-bodied. Therefore, they did not leave behind many noteworthy traces.
Geological activity has also caused the destruction of many traces of ancient life.
Because of this, scientists cannot be certain about the origins of life on Earth.
Stages in fossilization
Death
Rapid burial
Low oxygen environment
Long period of time
Rock replaces boy tissues
Fossil is formed
Fossil is discovered
Carl Woese proposed the 3 domain system. This classifies organisms based on chemical analysis. (3 kingdoms)
- Archaea (primitive bacteria usually living in extreme environments)
- Bacteria (true bacteria)
- Eukaryota (which includes protists, fungi, plants and animals)
Traditional (Linnaean) classification system (King Phillip came over for good soup)
Kingdom
Phylum
Class
Order
Family
Genus
Species
Classification
placing organisms into groups so they can be studied and analyse alot easier.
Binomial naming system
“homo sapiens” in italics
homo- genes
sapiens- species.
Evolutionary trees
Evolutionary trees are a method used by scientists to show how they believe organisms are related.
They use DNA analysis for living organisms and fossil data for extinct organisms.
Ecosystem
All of the living and non living factors within an environment
Abiotic
Abiotic (non-living) factors which can affect a community are:
* light intensity
* temperature
* moisture levels
* soil pH and mineral content
* wind intensity and direction
* carbon dioxide levels for plants
* oxygen levels for aquatic animals.
Biotic
Biotic (living) factors which can affect a community are:
* availability of food
* new predators arriving
* new pathogens
* one species outcompeting another so the numbers are no
longer sufficient to breed.
What happens if there are too many organisms competing for the same resources?
Only those best adapted to their habitat will survive.
Evolutionary trees
see picture
Different levels of organisations
-Organisms (individual species)
-Population ( no. of particular species living in a habitat)
-Community ( lots of different populations living in the area)
-Ecosystem ( interaction of a community of living organisms with non living parts of the environment)
Organisms are interdependent with other organisms
Pollination- many plants rely on insects (bees) for pollination
Seed dispersal- animals may carry plant seeds away from parent plant to reduce competition
Food- pandas rely on bamboos for food.
Adaptations
features or characteristics that allow an organism to live in their environment are known as their adaptations.
3 types of adaptations
Structural adaptations (anatomical)- physical features
Behavioural adaptation-
How the animal behaves
Functional adaptations (Physiological)- changes or chemical reactions in the organism. eg hybernate
Trophic level
level within a food chain / web that an organism occupies.
