Sciences · Topic 2.1
Genetics, Biotechnology, and Ecosystems
This topic covers the mechanisms of inheritance, the revolutionary tools of modern biotechnology, and how living systems maintain stability in ecosystems. These are high-priority topics in the eAssessment, which tests both scientific knowledge and the ability to evaluate social, ethical, and environmental impacts.
What You'll Learn
- Explain DNA structure, protein synthesis, and Mendelian inheritance patterns
- Describe and evaluate genetic engineering, GMOs, and CRISPR technology
- Analyse ecosystem dynamics: food webs, population growth, carrying capacity
- Explain homeostasis and negative feedback mechanisms
- Evaluate the benefits, risks, and ethics of biotechnology from multiple perspectives
- Interpret data from graphs and tables showing population dynamics
eAssessment Focus
Criterion A (Knowing): Define terms precisely; explain mechanisms (e.g., how negative feedback works).
Criterion B (Inquiring): Evaluate hypotheses; suggest improvements to experimental designs; interpret data.
Criterion C (Processing): Draw valid conclusions from data; identify patterns in population graphs.
Criterion D (Reflecting): Evaluate impacts from scientific, social, ethical, and environmental perspectives. One-sided answers score maximum 4.
Key Vocabulary
| Term | Definition |
|---|---|
| DNA | Deoxyribonucleic acid — the molecule carrying genetic information in cells |
| Gene | A segment of DNA that codes for a specific protein or trait |
| Allele | A variant form of a gene; e.g., dominant (A) or recessive (a) |
| Genotype | The genetic makeup of an organism (e.g., Aa, BB) |
| Phenotype | The observable traits of an organism resulting from genotype + environment |
| Genetic engineering | Deliberate modification of an organism's genome using biotechnology |
| CRISPR | A precise gene-editing tool allowing targeted cuts and modifications in DNA |
| Biodiversity | The variety of life in an area — genetic, species, and ecosystem diversity |
| Carrying capacity (K) | The maximum population size an environment can sustainably support |
| Homeostasis | Maintenance of a stable internal environment despite external changes |
| Negative feedback | A control mechanism that reverses a change to restore equilibrium |
| Positive feedback | A mechanism that amplifies a change (rare in homeostasis; e.g., blood clotting) |
Sciences · Topic 2.1
Genetics & Heredity
Genetics is the study of how traits are inherited. Understanding DNA, protein synthesis, and Mendelian inheritance patterns is essential for interpreting genetic data in the eAssessment.
DNA and Protein Synthesis
DNA Structure
Double helix of nucleotides. Each nucleotide: sugar + phosphate + base. Bases pair: A–T, C–G (complementary base pairing).
Transcription
DNA → mRNA in the nucleus. The coding strand is read; a complementary mRNA strand is built (T replaced by U in RNA).
Translation
mRNA → Protein at the ribosome. Each codon (3 bases) codes for one amino acid. The sequence of amino acids determines the protein.
Mutation
A change in the DNA sequence. Can be beneficial, neutral, or harmful. Most are neutral; some cause genetic diseases.
Mendelian Inheritance
Punnett Square Rules
Dominant (A) allele masks recessive (a) allele.AA or Aa → dominant phenotype expressed
aa → recessive phenotype expressed
Monohybrid Cross Example
Cross between two heterozygous parents (Aa × Aa):
| A | a | |
|---|---|---|
| A | AA | Aa |
| a | Aa | aa |
Genotype ratio: 1 AA : 2 Aa : 1 aa — Phenotype ratio: 3 dominant : 1 recessive
Inheritance Patterns
| Pattern | Description | Example |
|---|---|---|
| Dominant/Recessive | One allele masks the other | Brown eyes (B) dominant over blue (b) |
| Codominance | Both alleles expressed equally | Blood type AB |
| Sex-linked | Gene on X chromosome; affects males more | Colour blindness, haemophilia |
| Incomplete dominance | Intermediate phenotype in heterozygote | Red + white flower → pink |
eAssessment Tip: When drawing or interpreting a Punnett square, always state the gametes clearly, show the cross, and list both the genotype ratio AND phenotype ratio. Incomplete Punnett squares lose marks.
Sciences · Topic 2.1
Biotechnology
Biotechnology uses biological systems and living organisms to develop products and technologies. Modern tools like CRISPR represent a revolution in medicine and agriculture — but raise profound ethical questions.
Genetic Engineering Methods
Recombinant DNA
Cutting DNA from one organism and inserting it into another using restriction enzymes and vectors (plasmids). Used to produce insulin, vaccines.
PCR (Polymerase Chain Reaction)
Amplifies small DNA samples into millions of copies. Used in forensics, disease diagnosis, COVID-19 testing.
CRISPR-Cas9
A precise "molecular scissors" tool. Guide RNA directs Cas9 protein to cut specific DNA sequences. More precise, cheaper, and faster than older methods.
GMO Crops
Genetically Modified Organisms engineered for pest resistance, drought tolerance, or nutritional enhancement (e.g., Golden Rice — vitamin A enriched).
Benefits and Risks of Genetic Engineering
| Benefits | Risks / Concerns |
|---|---|
| Disease-resistant crops → food security | Unintended ecological consequences |
| Medical treatments (insulin, gene therapy) | Ethical concerns about "designer babies" |
| Bioremediation (cleaning pollution) | Unknown long-term effects on biodiversity |
| Drought-resistant crops | Corporate monopolisation of food supply |
| CRISPR treatment of sickle cell anaemia | Off-target edits causing unintended mutations |
| Reduced pesticide use | Herbicide-resistant "superweeds" developing |
Criterion D Strategy: Evaluating Biotechnology
For maximum marks, evaluate from four perspectives:
- Scientific: Does it work? What does the evidence show? What are the uncertainties?
- Ethical: Is it right? Whose consent matters? What about future generations?
- Environmental: What are the ecological impacts? Biodiversity effects?
- Social/Economic: Who benefits? Who has access? Are there justice issues?
Sciences · Topic 2.1
Ecosystems, Population Dynamics & Homeostasis
Ecosystems are complex systems of interacting organisms and their environments. Understanding how populations change and how organisms regulate their internal environment is crucial for environmental science questions.
Population Growth Models
Exponential Growth
J-shaped curve. Population grows at constant rate when resources are unlimited. Rate ∝ population size. Rare in nature long-term.
Logistic Growth
S-shaped (sigmoidal) curve. Growth slows as population approaches carrying capacity (K). More realistic model for most populations.
Carrying Capacity (K)
Maximum population size the environment can support. Limited by food, water, space, light, predation. Population stabilises at or oscillates around K.
Limiting Factors
Density-dependent: competition, predation, disease. Density-independent: temperature, natural disasters, climate events.
Food Webs and Energy Flow
10% Rule
Only ~10% of energy is transferred from one trophic level to the next. 90% is lost as heat, waste, and respiration.
This means food chains are typically limited to 4–5 levels. A herbivore gets 10% of a plant's energy; a carnivore gets 1% of that plant's original energy.
Homeostasis and Negative Feedback
- Receptor detects a change (e.g., body temperature rises above 37°C)
- Control centre (hypothalamus) processes the signal
- Effector responds (sweat glands produce sweat; blood vessels dilate)
- Result: temperature falls back toward set point (37°C)
- Receptor detects return to normal → response is switched off
Examples of Negative Feedback
| System | Change detected | Response | Effect |
|---|---|---|---|
| Thermoregulation | Body temp rises | Sweating, vasodilation | Temperature falls |
| Thermoregulation | Body temp falls | Shivering, vasoconstriction | Temperature rises |
| Blood glucose | Glucose rises | Insulin released by pancreas | Glucose falls |
| Blood glucose | Glucose falls | Glucagon released by pancreas | Glucose rises |
Key Distinction: Negative feedback counteracts change and restores equilibrium (most homeostatic mechanisms). Positive feedback amplifies change (used in specific processes: blood clotting, childbirth contractions, nerve impulse transmission). Do not confuse these.
Sciences · Topic 2.1
Ethical & Environmental Impacts
The eAssessment Criterion D requires you to reflect on the impacts of science on society and the environment. This section prepares you to write high-quality multi-perspective evaluations.
Science, Ethics and Society Framework
For any scientific issue, evaluate from:
Scientific perspective: What does the evidence show? What are the limitations/uncertainties of the science?
Ethical perspective: What are the rights and duties involved? Whose interests matter? Is consent possible?
Environmental perspective: What are the ecological consequences? Effects on biodiversity, ecosystems, climate?
Social/Economic perspective: Who benefits? Who bears the risks? Are the benefits equitably distributed?
Biodiversity — Why It Matters
Genetic Diversity
Variation within a species allows adaptation to environmental changes. Low genetic diversity → vulnerable to disease (e.g., monoculture crops).
Species Diversity
Number of different species in an ecosystem. More species → more stable ecosystem (resilient to disturbance).
Ecosystem Services
Benefits humans get from ecosystems: clean water, oxygen, pollination, climate regulation, food. These depend on biodiversity.
Threats to Biodiversity
Habitat destruction, pollution, invasive species, climate change, overexploitation. Genetic engineering can help or harm.
eAssessment Rule: A Criterion D answer that presents only benefits or only risks cannot score above 4/8. You must present multiple perspectives and reach a justified conclusion that goes beyond "it depends."
Sciences · Topic 2.1
Worked Examples
These examples model the response quality expected in the eAssessment, from data interpretation to extended evaluation.
PUNNETT SQUARETwo parents are both carriers of cystic fibrosis (Ff). Draw a Punnett square and find the probability that a child has cystic fibrosis.
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Full Solution
CF is autosomal recessive. Normal (F) is dominant; CF allele (f) is recessive.
Parents: Ff × Ff
Punnett square:
F f
F | FF | Ff
f | Ff | ff
Genotype ratio: 1FF : 2Ff : 1ff
Phenotype ratio: 3 unaffected : 1 affected
Probability of cystic fibrosis (ff) = 1/4 = 25%
Probability of being a carrier (Ff) = 2/4 = 50%
Probability of being unaffected non-carrier (FF) = 1/4 = 25%
Parents: Ff × Ff
Punnett square:
F f
F | FF | Ff
f | Ff | ff
Genotype ratio: 1FF : 2Ff : 1ff
Phenotype ratio: 3 unaffected : 1 affected
Probability of cystic fibrosis (ff) = 1/4 = 25%
Probability of being a carrier (Ff) = 2/4 = 50%
Probability of being unaffected non-carrier (FF) = 1/4 = 25%
EVALUATEEvaluate the benefits and limitations of using CRISPR technology in medicine.
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Full Solution
Benefits: CRISPR allows unprecedented precision in editing specific genes, offering potential treatments for previously incurable genetic diseases such as sickle cell anaemia and cystic fibrosis. Early clinical trials have shown promising results. Economically, successful gene therapies could reduce long-term healthcare costs. Environmentally, CRISPR could be used to control invasive species or revive extinct species that maintained ecosystem balance.
Limitations: "Off-target" edits can occur — unintended genetic changes that may cause new mutations or cancers. Ethically, germline (embryo) editing raises concerns about heritable changes that future generations cannot consent to, and about the potential for eugenics. Socially, the high cost of gene therapy may be accessible only to wealthy individuals or nations, exacerbating health inequalities.
Conclusion: CRISPR holds significant medical promise, but its deployment requires robust international regulation, ethical oversight, and equitable access frameworks before widespread clinical use. The technology itself is not inherently harmful or beneficial — the outcomes depend on governance.
Limitations: "Off-target" edits can occur — unintended genetic changes that may cause new mutations or cancers. Ethically, germline (embryo) editing raises concerns about heritable changes that future generations cannot consent to, and about the potential for eugenics. Socially, the high cost of gene therapy may be accessible only to wealthy individuals or nations, exacerbating health inequalities.
Conclusion: CRISPR holds significant medical promise, but its deployment requires robust international regulation, ethical oversight, and equitable access frameworks before widespread clinical use. The technology itself is not inherently harmful or beneficial — the outcomes depend on governance.
DATAA population graph shows a J-shaped curve followed by a rapid decline. Interpret this pattern.
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Full Solution
The initial J-shaped curve represents exponential growth — the population is growing without significant limiting factors, with resources abundant relative to population size.
The subsequent rapid decline is a population crash, likely caused by the population exceeding its carrying capacity (K). Once the population overshoots K, resources (food, water, space) are depleted faster than they can recover. This leads to starvation, increased disease, and competition, causing a rapid fall in numbers.
This "boom and bust" pattern is common in environments with time-lag responses, such as predator-prey relationships (Lotka-Volterra model) or bacteria in a finite medium.
The subsequent rapid decline is a population crash, likely caused by the population exceeding its carrying capacity (K). Once the population overshoots K, resources (food, water, space) are depleted faster than they can recover. This leads to starvation, increased disease, and competition, causing a rapid fall in numbers.
This "boom and bust" pattern is common in environments with time-lag responses, such as predator-prey relationships (Lotka-Volterra model) or bacteria in a finite medium.
EXPLAINExplain how negative feedback maintains blood glucose levels after a meal.
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Full Solution
Step 1 (Stimulus): After eating, glucose from digested carbohydrates is absorbed into the bloodstream. Blood glucose rises above the set point (~4.5–7.0 mmol/L).
Step 2 (Receptor): Specialised beta cells in the pancreas detect the elevated blood glucose.
Step 3 (Response): Beta cells secrete insulin into the bloodstream. Insulin signals body cells (especially liver and muscle cells) to take up glucose and convert it to glycogen (glycogenesis) for storage.
Step 4 (Negative feedback): As blood glucose falls back toward the set point, insulin secretion decreases. This prevents glucose from falling too low.
This is negative feedback because the response (insulin → lower glucose) opposes the original change (rising glucose).
Step 2 (Receptor): Specialised beta cells in the pancreas detect the elevated blood glucose.
Step 3 (Response): Beta cells secrete insulin into the bloodstream. Insulin signals body cells (especially liver and muscle cells) to take up glucose and convert it to glycogen (glycogenesis) for storage.
Step 4 (Negative feedback): As blood glucose falls back toward the set point, insulin secretion decreases. This prevents glucose from falling too low.
This is negative feedback because the response (insulin → lower glucose) opposes the original change (rising glucose).
ANALYSEA student claims GMO crops will solve global food security. Evaluate this claim.
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Full Solution
Evidence supporting the claim: GMO crops with drought tolerance (e.g., Bt cotton, drought-resistant maize) have increased yields in water-stressed regions. Pest-resistant crops reduce crop losses. Golden Rice provides vitamin A to combat deficiency diseases in Southeast Asia.
Limitations of the claim: Food insecurity is primarily a problem of distribution and poverty, not just production. GMOs do not address the political, economic, and logistical barriers to food access. Additionally, GMO crops are often patented by corporations, creating dependency for smallholder farmers. Ecological risks (herbicide-resistant weeds, loss of biodiversity) could undermine long-term food security.
Conclusion: The claim oversimplifies the issue. GMOs are one tool among many; they can contribute to food security but cannot solve it alone without addressing structural poverty, distribution systems, and ecological sustainability.
Limitations of the claim: Food insecurity is primarily a problem of distribution and poverty, not just production. GMOs do not address the political, economic, and logistical barriers to food access. Additionally, GMO crops are often patented by corporations, creating dependency for smallholder farmers. Ecological risks (herbicide-resistant weeds, loss of biodiversity) could undermine long-term food security.
Conclusion: The claim oversimplifies the issue. GMOs are one tool among many; they can contribute to food security but cannot solve it alone without addressing structural poverty, distribution systems, and ecological sustainability.
CALCULATEA food chain is: Grass → Rabbit → Fox → Eagle. If grass contains 100,000 kJ of energy, how much energy does the eagle receive?
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Full Solution
Using the 10% rule for each trophic level transfer:
Grass = 100,000 kJ
Rabbit receives 10% of grass = 10,000 kJ
Fox receives 10% of rabbit = 1,000 kJ
Eagle receives 10% of fox = 100 kJ
The eagle receives only 0.1% of the original energy in the grass, illustrating why food chains are limited in length and why ecosystems can support far fewer top predators than primary producers.
Grass = 100,000 kJ
Rabbit receives 10% of grass = 10,000 kJ
Fox receives 10% of rabbit = 1,000 kJ
Eagle receives 10% of fox = 100 kJ
The eagle receives only 0.1% of the original energy in the grass, illustrating why food chains are limited in length and why ecosystems can support far fewer top predators than primary producers.
SUGGESTA student conducts an experiment testing the effect of fertiliser concentration on algae growth but does not control light intensity. Suggest why this is a problem and how to improve the experiment.
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Full Solution
Problem: Light intensity is a confounding variable — it also affects algae growth. If light intensity varies between trials, the student cannot conclude that differences in algae growth are caused by fertiliser concentration alone. The results would be unreliable and invalid.
Improvements:
1. Conduct all trials in the same location with identical, constant artificial lighting.
2. Use identical transparent containers so light penetration is the same.
3. Monitor and record light intensity using a lux meter and ensure it remains constant throughout the experiment.
4. Conduct repeated trials at each fertiliser concentration to increase reliability.
Improvements:
1. Conduct all trials in the same location with identical, constant artificial lighting.
2. Use identical transparent containers so light penetration is the same.
3. Monitor and record light intensity using a lux meter and ensure it remains constant throughout the experiment.
4. Conduct repeated trials at each fertiliser concentration to increase reliability.
Sciences · Topic 2.1
Practice Q&A
Attempt each question before revealing the model answer. For evaluation questions, aim for at least two perspectives.
DEFINEWhat is the difference between genotype and phenotype? Give an example.
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Model Answer
Genotype: the genetic makeup of an organism, written as allele combinations (e.g., Aa, BB, tt).
Phenotype: the observable traits that result from the genotype interacting with the environment.
Example: A pea plant with genotype Tt (tall allele T dominant) has the phenotype "tall," but a plant with genotype tt has the phenotype "short." Both Tt and TT share the same "tall" phenotype.
Phenotype: the observable traits that result from the genotype interacting with the environment.
Example: A pea plant with genotype Tt (tall allele T dominant) has the phenotype "tall," but a plant with genotype tt has the phenotype "short." Both Tt and TT share the same "tall" phenotype.
EXPLAINWhat is CRISPR-Cas9 and why is it considered more useful than older genetic engineering methods?
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Model Answer
CRISPR-Cas9 is a gene-editing technology adapted from a natural bacterial immune system. A guide RNA directs the Cas9 enzyme to cut DNA at a precise location; the cell's repair mechanisms can then delete, replace, or modify the gene at that site.
It is superior to older methods because it is: more precise (targets specific sequences), cheaper (significantly lower cost than previous tools), faster (weeks vs years), and versatile (works in many organisms). These advantages make it revolutionary for medicine and agriculture.
It is superior to older methods because it is: more precise (targets specific sequences), cheaper (significantly lower cost than previous tools), faster (weeks vs years), and versatile (works in many organisms). These advantages make it revolutionary for medicine and agriculture.
INTERPRETDescribe what an S-shaped population growth curve tells you about the relationship between population size and resources.
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Model Answer
An S-shaped (logistic) curve shows three phases. Initially, growth is exponential (rapid increase) when population is small relative to resources. As the population grows, limiting factors (food, space, water) become more significant — growth rate slows. Finally, the population stabilises at or near the carrying capacity (K), where birth rate equals death rate.
This demonstrates that population growth is ultimately constrained by resource availability. Larger populations experience more competition and face stronger environmental resistance, which is captured by the logistic model.
This demonstrates that population growth is ultimately constrained by resource availability. Larger populations experience more competition and face stronger environmental resistance, which is captured by the logistic model.
EVALUATEA country plans to introduce a genetically engineered mosquito that cannot reproduce, to reduce malaria transmission. Evaluate the use of this technology.
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Model Answer
Benefits: Malaria kills ~600,000 people annually. Reducing mosquito populations could save lives and reduce healthcare costs, especially in Sub-Saharan Africa. Unlike chemical pesticides, this approach is species-specific and avoids chemical residues in ecosystems.
Risks: Eliminating a mosquito species could disrupt food webs (mosquitoes are food for birds, bats, and fish). There is scientific uncertainty about long-term ecological effects. Ethically, permanently altering an ecosystem raises questions about consent from affected communities and future generations. Practically, other mosquito species may fill the niche.
Conclusion: Given the scale of malaria mortality, the potential benefits are substantial, but deployment should involve extensive ecological risk assessment, community consultation, and staged pilot programmes before large-scale release.
Risks: Eliminating a mosquito species could disrupt food webs (mosquitoes are food for birds, bats, and fish). There is scientific uncertainty about long-term ecological effects. Ethically, permanently altering an ecosystem raises questions about consent from affected communities and future generations. Practically, other mosquito species may fill the niche.
Conclusion: Given the scale of malaria mortality, the potential benefits are substantial, but deployment should involve extensive ecological risk assessment, community consultation, and staged pilot programmes before large-scale release.
SUGGESTSuggest two ways in which a loss of biodiversity might reduce an ecosystem's ability to recover from drought.
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Model Answer
1. Reduced functional redundancy: In a biodiverse ecosystem, multiple species perform the same ecological function (e.g., pollination). If one species is lost to drought, others can maintain the function. Low biodiversity means fewer "backup" species, making the ecosystem more vulnerable.
2. Reduced genetic variation: A species with high genetic diversity is more likely to contain individuals with drought-resistant traits that survive and rebuild the population. Low genetic diversity means the entire species may die if conditions exceed their tolerance range.
2. Reduced genetic variation: A species with high genetic diversity is more likely to contain individuals with drought-resistant traits that survive and rebuild the population. Low genetic diversity means the entire species may die if conditions exceed their tolerance range.
INHERITANCERed-green colour blindness is X-linked recessive. A carrier mother (XNXn) and a normal father (XNY) have children. What is the probability of a colour-blind son?
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Model Answer
Punnett square for X-linked trait:
XN Xn
XN| XNXN | XNXn
Y | XNY | XnY
Offspring: 1 normal female : 1 carrier female : 1 normal male : 1 colour-blind male
Probability of a colour-blind son = 1/4 = 25%
(But probability of a son being colour-blind = 1/2 = 50%, because half the sons receive Xn)
XN Xn
XN| XNXN | XNXn
Y | XNY | XnY
Offspring: 1 normal female : 1 carrier female : 1 normal male : 1 colour-blind male
Probability of a colour-blind son = 1/4 = 25%
(But probability of a son being colour-blind = 1/2 = 50%, because half the sons receive Xn)
APPLYExplain why biological control (using natural predators) is generally preferred over pesticides from an environmental perspective.
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Model Answer
Pesticides have several environmental disadvantages: they can accumulate up food chains (bioaccumulation and biomagnification), killing non-target organisms including pollinators; they can leach into waterways, harming aquatic ecosystems; pests can develop resistance; and they break down slowly in soil.
Biological control introduces natural predators, parasites, or pathogens that target the pest specifically, reducing chemical pollution. Once established, control agents can self-sustain. However, introducing non-native species risks unintended ecological consequences if the control agent itself becomes invasive. Careful risk assessment is required.
Biological control introduces natural predators, parasites, or pathogens that target the pest specifically, reducing chemical pollution. Once established, control agents can self-sustain. However, introducing non-native species risks unintended ecological consequences if the control agent itself becomes invasive. Careful risk assessment is required.
HOMEOSTASISWhy is maintaining a constant body temperature important for enzyme function?
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Model Answer
Enzymes are proteins with a specific three-dimensional active site. Their function depends on the shape of this active site matching the substrate. Temperature affects enzyme activity: too low, and reaction rate slows as molecules have less kinetic energy. Too high, and the enzyme denatures — the active site changes shape irreversibly and the enzyme stops functioning.
Most human enzymes have an optimal temperature of approximately 37°C. Homeostatic thermoregulation maintains this temperature, ensuring enzymes operate at peak efficiency for all metabolic processes. Deviations (fever >40°C or hypothermia) are life-threatening precisely because enzyme function is compromised.
Most human enzymes have an optimal temperature of approximately 37°C. Homeostatic thermoregulation maintains this temperature, ensuring enzymes operate at peak efficiency for all metabolic processes. Deviations (fever >40°C or hypothermia) are life-threatening precisely because enzyme function is compromised.
Sciences · Review
Flashcard Review
Tap each card to reveal the answer. Try to answer from memory first.
What is CRISPR-Cas9?
A precise gene-editing tool that uses guide RNA to direct the Cas9 enzyme to cut specific DNA sequences, allowing deletion, insertion, or modification of genes.
Tap to reveal
What is the difference between genotype and phenotype?
Genotype: the allele combination an organism carries (e.g., Aa). Phenotype: the observable traits expressed (e.g., brown eyes). Phenotype = genotype + environment.
Tap to reveal
What is carrying capacity (K)?
The maximum population size that an environment can sustainably support, limited by resources such as food, water, and space.
Tap to reveal
What is negative feedback in homeostasis?
A control mechanism that opposes a change to restore the system to its set point (equilibrium). Example: rising body temperature triggers sweating and vasodilation to cool down.
Tap to reveal
What is the 10% rule in energy flow?
Only approximately 10% of energy is transferred from one trophic level to the next; 90% is lost as heat, movement, and waste.
Tap to reveal
What is codominance? Give an example.
Both alleles are fully expressed in the heterozygote. Example: blood type AB — both A and B antigens are produced; neither is dominant.
Tap to reveal
Why must Criterion D evaluations include multiple perspectives?
One-sided responses cannot score above 4/8. You must evaluate scientific, ethical, environmental, and social/economic impacts to reach the highest bands.
Tap to reveal
What is biodiversity and why does it matter?
The variety of life at genetic, species, and ecosystem levels. High biodiversity = more stable, resilient ecosystems with greater capacity to provide ecosystem services.
Tap to reveal
What does insulin do in blood glucose regulation?
Insulin (released by pancreatic beta cells when blood glucose rises) signals body cells to take up glucose and liver cells to convert glucose to glycogen, lowering blood glucose.
Tap to reveal
What causes a J-shaped population growth curve?
Exponential growth when resources are unlimited (or sufficient) relative to population size. Each individual reproduces at a constant rate, so growth rate increases with population.
Tap to reveal
What is bioaccumulation?
The build-up of a toxic substance in an organism's tissues over time. Biomagnification occurs when concentrations increase at each higher trophic level in a food chain.
Tap to reveal
What is a confounding variable?
An uncontrolled variable that affects the dependent variable independently of the independent variable, making it impossible to determine the true cause of results.
Tap to reveal
What is sex-linked inheritance?
Inheritance of a gene located on a sex chromosome (usually X). X-linked recessive traits (e.g., colour blindness) appear more often in males (XY) because they have only one X.
Tap to reveal
What is recombinant DNA technology?
Cutting DNA from one organism using restriction enzymes and inserting it into another organism's DNA (often via a plasmid vector), so the recipient organism produces a new protein.
Tap to reveal
Describe the difference between exponential and logistic growth.
Exponential: J-shaped, unlimited growth (no resource constraints). Logistic: S-shaped, growth slows as population approaches carrying capacity K due to limiting factors.
Tap to reveal
Sciences · Practice Test
Practice Test — 20 Questions
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