Body Organization, Transport & Movement — Problem set, Grade 7
Five focused units, a three-session investigation, chapter review, and chapter quiz.
Review the key ideas
Levels of Organization: Cells to Organ Systems
Multicellular organisms contain cells that perform specialized roles. Cells working together form tissues; an organ combines several tissue types; an organ system includes organs interacting in a larger function. An organism is the whole living individual. This hierarchy organizes relationships rather than saying each level works independently.
Digestion, Absorption & Food Molecules
Digestion breaks food into smaller components that can be absorbed and used. Mechanical processes such as chewing change size; chemical digestion changes large molecules into smaller molecules through reactions. Enzymes help these reactions occur. Digestion does not simply convert food directly into blood or energy.
Circulatory & Respiratory Systems
The respiratory system moves air and exchanges gases; the circulatory system transports materials between organs and cells. In lungs, oxygen moves from air spaces into blood while carbon dioxide can move in the other direction. The heart pumps blood through vessels. These tasks interact, but ventilation, gas exchange, and cellular respiration are distinct processes.
Bones, Muscles & Structure-Function Models
Animal movement involves support structures, muscles, joints, and coordination. Bones provide support, protect some organs, and form parts of movable arrangements. Skeletal muscles contract and pull through connections such as tendons. A contraction can produce movement only in relation to the structures and forces involved.
Kidneys, Excretion & Internal Balance
Cells produce waste materials through metabolism, and organisms regulate internal water and dissolved substances. Excretion removes metabolic wastes; it differs from elimination of unabsorbed food from the digestive tract. Lungs release carbon dioxide, while kidneys help remove some dissolved wastes and regulate blood composition.
Problem 1
Answer and explanation
The digestive system processes and absorbs food molecules, the circulatory system transports them, and muscle cells use them in cellular work. Organs contain interacting tissues, and tissues contain specialized cells. The pathway connects levels and systems; neither an intestine nor a muscle cell independently performs every step. The diagram is a selected model, not a complete anatomical description.
Identify digestive and circulatory organ-system roles.
Locate exchange surfaces within organs and tissues.
Connect transport to cellular use.
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
Answer and explanation
It combines several tissue types that contribute different roles to pumping and maintaining its structure.
Problem 3
Answer and explanation
Faster breakdown in B is consistent with increased exposed surface for enzyme contact under the stated conditions. The result is evidence about breakdown rate, not proof that absorption or energy use has already occurred. Further measurements could check the products and their passage across an exchange surface. Other changed conditions would weaken the isolated surface-area explanation.
Identify comparable mass and conditions.
Connect smaller pieces with more exposed surface.
Separate breakdown from later boundary crossing.
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
Answer and explanation
It changes piece size and surface area but does not necessarily break the relevant chemical bonds into absorbable components.
Problem 5
Answer and explanation
Oxygen enters lung air spaces, crosses into blood, is transported through the heart and vessels, and reaches tissues by exchange. Carbon dioxide can follow a return pathway toward lung release. Cellular respiration occurs in cells and uses food and oxygen in the aerobic model; it is not simply the act of breathing. The diagram is simplified and does not show every anatomical detail.
Add lung exchange into blood.
Add heart and transport vessels.
Add tissue exchange and cellular use.
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
Answer and explanation
No. It remains a mixture including nitrogen, oxygen, carbon dioxide, and water vapor in different proportions.
Problem 7
Answer and explanation
The strings represent pulls that can rotate the hinge in opposite directions, analogous to coordinated muscle actions. The model does not show nerves, living tissue, energy transfers, changing forces, or exact anatomical scale. It illustrates a mechanical relationship without establishing individual performance or health.
Identify the hinge as a turning point.
Connect each pull with an opposing action.
State missing tissues and cellular processes.
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
Answer and explanation
It identifies parts but does not explain how their arrangement contributes to support, protection, or movement.
Problem 9
Answer and explanation
The model balances its 100 input units with 100 output units, and 96% return through the stated pathway. It represents selective processing rather than all filtrate being excreted. The numbers are invented for one boundary and interval; they do not describe a person’s whole water budget or prescribe fluid intake.
Add outputs: 96+4=100.
Calculate returned share: 96/100×100%.
Identify the simplified boundary and invented units.
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
Answer and explanation
Excretion removes wastes produced by metabolism; unabsorbed food is material that did not enter those cellular pathways.