Unit 2B Flashcards
Characteristics
Features such as eye colour, which are determined by proteins made by genes.
We inherit different combinations of chromosomes (and therefore genes) from our parents, making us unique.
Karyotype
The pattern made by breaking open the nucleus of a cell and lining the chromosomes up in matching pairs.
Fertilisation (human)
Occurs when the nucleus of an egg (23 chromosomes) combines with the nucleus of a sperm (23 chromosomes) to create a zygote (46 chromosomes).
Alleles
The different versions of a gene. eg. the eye colour gene has 3 alleles - brown, green and blue
The 2 chromosomes in a pair carry the same gene, but the alleles may be different.
Genotype
A 2 letter code indicating which alleles you have inherited from each parent (for a single gene) eg. BB
Capital letter = dominant allele, lower case letter = recessive allele.
Phenotype
Describes how a gene is expressed.
Often appearance (eg. eye colour) but not always (eg. blood type).
Monohybrid cross
Used to study how the alleles of 2 parents recombine in the offspring, for a single gene.
eg. BB x bb
Punnett square
A table used in a monohybrid cross to recombine gametes.
F1 generation
The offspring created in the original cross.
F2 generation
The offspring created by breeding 2 members of the F1 generation together.
Continuous variation
Variation that is controlled by many genes.
Produces a range of data. eg. height which can be displayed as a histogram.
Discrete (discontinuous) variation
Variation that is controlled by a single gene.
Data falls into separate categories eg. blood type, tongue rolling and is displayed as a bar chart.
Annual plants
Complete their lifecycle in one year. eg. poppies
They survive the winter as dormant seeds which germinate in the spring.
They are small, fast growing, produce many lightweight seeds and can grow on poor soils.
Perennial plants
Do not die after one year - they regrow from existing plants. eg. trees
They grow slowly, producing large seeds. They can grow very tall over time, and need fertile soil.
Plant growth curve
Shows the change in dry mass of a plant over its lifecycle.
Mass decreases during germination as the food store is used up, increases when the plant carries out photosynthesis and grows new tissue, then decreases as seeds are shed.
Requirements for plant growth
Warm temperatures
Water
Sunlight
Nutrients - nitrogen, phosphorous and potassium (NPK) dissolved in water
Nutrient deficiency (plants)
If plants lack important nutrients, their leaves turn yellow and they have stunted growth (they don’t grow properly).
Nitrogen
Needed to build amino acids and proteins.
Phosphorous
Needed to build DNA and ATP (for cell reactions)
Potassium
Needed for photosynthesis
Human growth curve
Babies grow rapidly, then their growth rate slows down.
Boys and girls then have growth spurts during adolescence.
The steeper the graph, the faster the rate of growth.
Nature vs nurture
Your phenotype (characteristics) is determined by your genes and environment working together.
eg. you may inherit the alleles to be tall, but don’t grow tall due to a poor diet.
Twin studies
Identical twins separated at birth can be used to study the effects of environment on phenotype (as they are genetically identical)
Malnutrition
Occurs as a result of a poor diet lacking in essential nutrients.
Deficiency diseases
Occur if a particular important nutrient is absent from the diet.
eg. vitamin D deficiency - rickets; vitamin C deficiency - scurvy; vitamin A deficiency - blindness; lack of iron - anaemia
Birth defects
Occur as a result of damage to the parents’ DNA or the DNA of the developing baby during pregnancy.
Damaged DNA is unable to produce proteins that function correctly.
DNA can be damaged by chemicals (eg. Agent Orange, Thalidomide) or radiation (eg. following the Chernobyl disaster).
External factors
Factors in the environment which can affect our bodies. eg. weather conditions, food availability, water
Internal factors
Conditions inside our bodies eg. blood glucose level, body temperature
Optimum conditions
The best conditions for enzyme action.
Allow the body to work efficiently.
Homeostasis
Mechanisms used to keep internal conditions constant.
Uses negative feedback loops.
Mechanisms to decrease body temperature
A rise in body temperature is detected by sensors (thermoreceptors) in our skin and blood vessels.
A signal is sent to the brain, which sends signals to sweat glands and blood vessels under the skin.
Sweat cools the skin as it evaporates.
Blood vessels widen, allowing hot blood to flow under the skin and lose heat by radiation.
Mechanisms to increase body temperature
A decrease in body temperature is detected by sensors (thermoreceptors) in our skin and blood vessels.
A signal is sent to the brain, which sends signals to hairs, muscles and blood vessels under the skin.
Hairs stand upright, and trap a layer of insulating air next to the skin.
Muscles contract rapidly, causing shivering, which generates heat.
Blood vessels narrow, preventing blood flow to the skin so less heat is lost.
Pancreas
An organ in the digestive system.
Contains receptors that detect changing levels of blood glucose.
Releases hormones to correct changes in blood glucose.
Hormones
Chemical signals that travel in the blood.
They target certain organs (which have the correct hormone receptors).
Insulin
A hormone released by the pancreas when blood glucose rises too high.
It targets liver cells, causing them to absorb glucose from the blood and store it.
This causes blood glucose levels to drop.
Glucagon
A hormone released by the pancreas when blood glucose falls too low.
It targets the liver, which releases stored glucose back into the blood.
This causes blood glucose levels to rise.
Type 1 diabetes
A serious disease caused when the body fails to produce insulin.
Blood glucose levels tend to fluctuate, and can get very high.
It is controlled by monitoring blood glucose levels and injecting insulin.
Type 2 diabetes
Insulin is still made, but the body stops responding to it and it has no effect, resulting in high blood glucose levels.
Caused by obesity and an unhealthy lifestyle.
Controlled by reducing sugar intake, exercise and eating healthy food.
