Year 8 Science · Unit 1 · Lesson 18
Challenge Worksheet
Learning Goals
1. Name the plant tissue that carries water up from the roots and the one that carries sugar from the leaves, and state which body system does the same kind of job in a human.
Read the data
A runner at rest and running hard
A sports scientist measured Sam’s breathing and heart at rest, then again while Sam was running hard on a treadmill.
| Measurement | At rest | Running hard |
|---|---|---|
| Breaths per minute | 12 | 40 |
| Air taken in with each breath (L) | 0.5 | 2.5 |
| Blood pumped by the heart per minute (L) | 5 | 20 |
Source: sample measurements for one runner.
2. Calculate the volume of air Sam breathes in per minute at rest and while running. Then work out how many times larger the air per minute and the blood per minute each become when Sam runs, and state which one rises more.
Answer times larger (air; blood)
3. Explain why both of these increase together when Sam runs. Use the problem-solving frame, starting from the muscle cells in Sam’s legs.
Find the errors
Lachlan’s answer: how the body’s systems work together
(1) The body is organised from cells into tissues, organs and organ systems. (2) The lungs are the pump that pushes blood through the blood vessels. (3) Most food is broken down and absorbed in the lungs. (4) The absorbed nutrients are carried to cells in the blood, so the digestive and circulatory systems work together. (5) The kidneys filter urea out of the blood, and it leaves the body in urine. (6) The lungs are also excretory organs, because they remove oxygen from the blood. (7) Oxygen moves from the alveoli into the blood because there is more oxygen in the blood than in the alveoli. (8) Because the systems are connected, a problem in one system always makes every other system stop working completely.
4. Five of the eight sentences contain a science error. Identify each one by its number, and write a corrected version.
| Sentence | Corrected version |
|---|---|
Plan an investigation
Depth-study question: Do leaves from the sunny side of a tree have more stomata than leaves from the shady side? You can count stomata by painting clear nail polish on a small patch of the lower surface of a leaf, peeling it off with clear sticky tape once dry, and looking at the peel under a microscope.
Prediction
If ... then ... because ...
Variables
Method
Evidence and trust
How will you record and present the results, and what will make them trustworthy?
5. Evaluate this claim: “In a living system, each part does its own job, so the parts do not really depend on each other.” Use Sam’s data, an example from plants and one idea from Lachlan’s answer (once corrected). End with your verdict.
Warm Up
1. Xylem (water) and phloem (sugar); the circulatory system. [2 marks: 1 both tissues, 1 system]
Read the data
2. Air: 12 × 0.5 = 6 L/min at rest; 40 × 2.5 = 100 L/min running; 100 ÷ 6 ≈ 17 times larger. Blood: 20 ÷ 5 = 4 times larger. Air per minute rises more. [4 marks: 1 each air value, 1 both ratios, 1 comparison]
3. Working muscle cells use more oxygen and make more carbon dioxide. The lungs take in more air so more oxygen enters the blood; the heart pumps more blood to carry it to the muscles and return carbon dioxide to the lungs. [3 marks: 1 cells’ need, 1 respiratory role, 1 circulatory link]
Find the errors
4. Errors are in sentences 2, 3, 6, 7 and 8. (2) The heart is the pump. (3) Food is digested in the stomach and small intestine and mostly absorbed in the small intestine. (6) The lungs remove carbon dioxide. (7) There is more oxygen in the alveoli than in the blood. (8) A problem can affect the systems that depend on it, but does not always stop them all. Sentences 1, 4 and 5 are correct. [5 marks: 1 per error found and corrected]
Plan an investigation
Prediction: e.g. sunny-side leaves have more stomata, as they take in more carbon dioxide in bright light (accept a reasoned opposite). Independent: sunny or shady side. Dependent: stomata per field of view. Controlled (any two): same tree, similar leaf age and size, same part of the lower surface, same magnification. Method: peel from each leaf; count three fields of view per peel. Evidence: table, averages, bar graph; five or more leaves per side.
Show What You Know
5. Marking guide (points expected): 1 each part has its own role; 1 Sam’s data: air per minute up about 17 times and blood 4 times, together, because muscle cells need both; 1 plant: roots take in water that xylem carries to the leaves, which make sugar that phloem carries to the roots; 1 corrected Lachlan idea (e.g. absorbed nutrients reach cells in the blood); 1 a problem in one part affects others without stopping everything; 1 judgement: claim wrong; separate roles, but the parts depend on each other. [6 marks]
Common error to watch for: in Question 2, finding the difference (100 − 6) instead of how many times larger (100 ÷ 6).