Coordination, Defense & Reproduction — Problem set, Grade 7

Five focused units, a three-session investigation, chapter review, and chapter quiz.

Review the key ideas

The Nervous System, Senses & Responses

The nervous system receives information, processes it, and helps coordinate responses. Receptors respond to particular stimuli, such as light or pressure, and signals travel through nervous pathways. The brain and spinal cord contribute to processing; nerves connect with other parts of the body. A sensory experience involves more than a receptor alone.

Homeostasis, Feedback & Interacting Systems

Homeostasis is regulation that keeps internal conditions within functioning ranges despite changes. Temperature, water balance, and other conditions can vary; homeostasis does not mean an organism never changes. Feedback connects detection of a condition with responses that affect that condition.

Microorganisms, Barriers & Immune Defense

Microorganisms include diverse cellular organisms, while viruses are infectious agents that depend on host cells for replication. Many microorganisms are harmless or helpful in particular settings; some can cause disease. “Microbe” is not a synonym for enemy, and a detection record does not automatically show illness.

Sexual & Asexual Reproduction

Reproduction produces new organisms through different biological processes. In many asexual processes, one parent contributes the inherited material without fusion of gametes. In sexual reproduction, gametes combine through fertilization. Offspring inherit material from contributing parents, but sexual reproduction does not mean offspring receive an equal visual blend of every characteristic.

Flowers, Seeds & Plant Life Cycles

Flowering plants reproduce through structures and processes connecting pollen transfer, fertilization, seeds, and growth. Pollen carries cells involved in producing or delivering male gametes; an ovule contains structures involved in female reproduction. Pollination moves pollen to a suitable receptive surface; fertilization is a later fusion event. These terms should not be used interchangeably.

Problem 1

Illustrative timing trials are 0.20, 0.25, and 0.30 seconds for one defined task. A draft labels the mean a complete measure of the person’s intelligence. Calculate mean and range, describe the measured pathway in general, and correct the claim.
Answer and explanation

Mean response time is 0.25 s and numerical range is 0.10 s. A stimulus-response task involves detection, processing, and action plus measurement conditions. These values cannot establish overall intelligence or health; attention, equipment, and task demands also matter. They describe only the supplied fictional trials.

Mean: 0.75/3=0.25 s.

Range: 0.30−0.20=0.10 s.

Separate the task measure from an unsupported personal conclusion.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 2

Is a receptor alone the whole sensory experience?
Answer and explanation

No. Signals and processing contribute to perception, interpretation, and response.

Problem 3

Illustrative artificial-system record: a quantity rises from 20 to 24 units; a detector activates an output that lowers it to 21. The stated working range is 19–22 units. Explain the direction of feedback, the final relation to the range, and why these are not human clinical values.
Answer and explanation

The response opposes the rise, so it represents negative feedback. The final 21 lies within the stated working range. The units and thresholds are invented for an artificial system; they do not evaluate a learner’s body. The model illustrates a relationship while omitting the complexity of living regulation.

Identify the initial rise.

Connect the activated output with the opposing decrease.

Compare 21 with the invented range.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 4

Does homeostasis require the same number at every instant?
Answer and explanation

No. Regulation can maintain functioning ranges while values vary with conditions.

Problem 5

Illustrative model: a response recognizes Symbol A; Symbol B differs; after repeated A exposure the model response begins faster. No clinical records are represented. Explain specific recognition and memory, distinguish the observation from a universal protection claim, and state a model limit.
Answer and explanation

The model illustrates target-specific recognition and a memory-related faster response to A. It does not establish an identical response to B or guaranteed protection in a real person. Matching symbols simplify molecular interactions and omit many defense pathways. The supplied pattern is educational evidence about the model, not a clinical assessment.

Identify the repeated target A.

Compare response timing under the stated model.

Avoid assigning the same result to B or every real infection.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 6

Are all bacteria disease-causing?
Answer and explanation

No. Bacteria have diverse roles, including many that are harmless or beneficial in particular contexts.

Problem 7

Illustrative organisms: A produces new individuals from parent tissue without gamete fusion; B begins with fusion of two gametes. A later develops one new mutation. Classify the mechanisms, explain how A can vary, and distinguish offspring production from successful reproduction over a life cycle.
Answer and explanation

A represents asexual reproduction and B sexual reproduction. A’s new mutation shows that asexual offspring are not guaranteed identical in every detail. The records describe production mechanisms, but later survival and reproductive success depend on development and conditions. More information is needed to compare outcomes, not merely count starting cells.

Identify no fusion in A and fusion in B.

Connect A’s new mutation with variation.

Consider later survival and reproductive stages.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 8

Does asexual reproduction forbid all variation?
Answer and explanation

No. Mutations and environmental effects can produce differences, even when offspring share much inherited material.

Problem 9

Illustrative seven-day data: Treatment A has 18 germinated seeds of 20; B has 12 of 20. Species and other conditions are stated matched; the treatment is water amount. Calculate both percentages, describe the measured difference, and qualify the claim about lifelong plant success.
Answer and explanation

A has 90% germination and B 60%, a 30-percentage-point difference in this illustrative comparison. It supports a treatment-related germination question under the matched conditions, but does not establish adult survival, universal species response, or every causal detail. Replicate independent groups and record later growth separately.

A: 18/20×100=90%.

B: 12/20×100=60%.

Difference is 30 percentage points.

Limit the claim to the stipulated germination interval.

Response criteria

  • Explain the relevant biological process accurately.
  • Use the supplied evidence and show calculation steps with units where needed.
  • Connect a labeled model or mechanism with the claim.
  • State an assumption, evidence limitation, or useful next observation.

Problem 10

Does observing a pollinator visit prove viable seeds formed?
Answer and explanation

No. The visit is one stage; transfer, compatibility, fertilization, and development need further evidence.

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