Scientific thinking
What is an independent variable?
The factor deliberately changed by the investigator.
What process moves water from oceans or lakes into the atmosphere as water vapour?
Evaporation
Evidence of an organism’s activity, such as a footprint or burrow.
Trace fossil
What is the name of the type of cell division that makes genetically identical body cells?
Mitosis.
What is a gene?
A section of DNA containing instructions for a functional product, such as a protein.
The measured outcome that may respond to the independent variable.
Dependent Variable
Name Earth’s four main internal layers from the outside in.
Crust, mantle, outer core, inner core.
What is natural selection?
Individuals with heritable traits suited to the environment are more likely to survive and reproduce, changing trait frequencies over generations.
The type of cell division that produces haploid gametes
What is the difference between genotype and phenotype?
Genotype is an organism’s allele combination; phenotype is its observable characteristic.
Why are controlled variables important in a fair test?
They help ensure any measured change can be linked to the independent variable, rather than other factors.
A community of organisms interacting with one another and with the non-living environment.
An ecosystem
What is the difference between a mould fossil and a cast fossil?
A mould is an impression or hollow; a cast forms when material fills that impression.
What do the terms haploid and diploid mean?
Haploid: one set of chromosomes (n). Diploid: two sets (2n).
Will also accept haploid is half the amount
Heterozygous
Having two different Alleles
A scientist wants to investigate whether the amount of water given to a plant affects its growth. Identify the independent variable, dependent variable and one controlled variable
Independent variable: Amount of water given to the plant.
Dependent variable: Plant growth (e.g. height in cm).
Controlled variable: Type of plant, amount of sunlight or type of soil.
Give one likely impact of climate change on ecosystems.
For example: shifting species ranges, altered rainfall, extreme heat, or habitat loss.
How do homologous structures provide evidence of evolution?
They share an underlying anatomical origin, indicating common ancestry, even when functions differ.
Why does meiosis usually produce genetically varied cells?
Crossing over and independent assortment create new combinations of alleles.
Two heterozygous parents (Aa × Aa) have offspring. What is the expected genotypic ratio?
1 AA : 2 Aa : 1 aa
A student tests whether fertiliser improves plant growth by giving one plant fertiliser and another plant no fertiliser. After two weeks, the fertilised plant is taller. Explain TWO reasons why the student cannot confidently conclude that fertiliser caused the difference.
Only one plant was used in each condition, making the results less reliable.
Other variables, such as sunlight, water or initial plant size, may not have been controlled.
Explain how increased greenhouse gases can lead to global warming.
They absorb and re-emit outgoing infrared radiation, reducing energy loss to space and warming Earth’s surface and lower atmosphere.
How do divergent and convergent evolution differ?
Divergent: related lineages develop different traits; convergent: distantly related lineages independently evolve similar traits.
Failure of chromosomes to separate properly during division; it can produce cells with abnormal chromosome numbers.
Non-disjunction
An unaffected father (XᴺY) and a mother affected by an X-linked recessive condition (XⁿXⁿ) have a child. What is the probability that a randomly selected child is an affected son?
50% of all children (all sons affected; daughters are carriers).