Year 8 Science · Unit 1 · Lesson 5
Challenge Worksheet
Learning Goals
Find the errors
This paragraph contains exactly four errors. Underline each one and write the correction below.
A student’s summary: an echidna and a waratah
All organisms are made of cells. In an echidna, many similar lining cells join together to form the stomach. A waratah leaf contains several different tissues, so it is an organ. Waratah cells have no mitochondria, because their chloroplasts do that job instead. The echidna’s heart is its whole circulatory system. The waratah has no organ systems, only separate parts that each work alone. Both organisms are organised from cells, to tissues, to organs, to organ systems.
1. Write the four corrections.
Real-world context: organ transplants
When an organ is donated, it is removed from the donor, packed in ice and rushed to the patient. Once it is cut off from the donor’s blood supply, the clock starts. Table 1 shows how long each organ can usually be stored before it must be transplanted.
| Organ | Organ system | Usual maximum storage time (hours) |
|---|---|---|
| Heart | Circulatory | 4 to 6 |
| Lungs | Respiratory | 4 to 6 |
| Liver | Digestive | 8 to 12 |
| Kidney | Excretory (urinary) | 24 to 36 |
Source: typical ranges quoted by organ donation services; the real limit depends on the organ and the donor.
2. Using the longest time for each, how many times longer can a kidney be stored than a heart?
Answer times
3. A donor heart is removed at 9:40 am. The trip to the hospital takes 2 hours 55 minutes, and preparing it for surgery takes another 50 minutes. At what time is it ready to transplant, and is this inside the shortest time limit in Table 1? Show your working.
Ready at time
4. Use the levels of organisation to explain why a heart can survive for only a few hours once it is removed from the body, even when it is kept cold. Start at the cell level.
Evaluate the claim
Someone claims
“The transplant data prove that the organ is the most important level of organisation. A person dies without a heart, but nobody dies from losing a few cells.”
5. Identify one part of the claim that is correct.
6. Explain what the claim leaves out. Refer to at least two other levels, and use Question 4 as evidence.
7. A student argues: “Plants are less organised than animals. A plant has no heart, no lungs and no brain, and you can cut a piece off a plant and it grows back, which would never happen with an animal’s leg.” Evaluate this argument. Use a named plant and a named animal, and compare them at the cell, tissue, organ and organ system levels.
Find the errors
1. (i) Similar lining cells form lining tissue; the stomach is an organ made of several tissues. (ii) Plant cells do have mitochondria as well as chloroplasts: chloroplasts make food, mitochondria release energy from it. (iii) The heart is one organ of the circulatory system, with the blood vessels and blood. (iv) The waratah has organ systems, the root and shoot systems, whose parts work together. [4 marks: 1 per correction]
Your Turn
2. 36 ÷ 6 = 6 times. [1 mark] 3. 2 h 55 min + 50 min = 3 h 45 min; 9:40 am + 3 h 45 min = 1:25 pm. The shortest heart limit is 4 h, so yes, with 15 minutes to spare. [3 marks: total; clock time; comparison]
4. Heart muscle cells need oxygen and food brought, and wastes taken away, by the blood. Removed from the body, the heart has no blood flowing through it, so its cells run short of oxygen and start to die; as cells die the muscle tissue is damaged and the organ can no longer pump. [3 marks: cells need blood supply; none outside the body; cell death damages tissue and organ]
Evaluate the claim
5. A person cannot survive without a working heart. [1 mark] 6. The heart only works because of other levels: it is made of muscle tissue made of cells, and Question 4 shows the organ fails once its cells lose their blood supply. It also needs the rest of its system (vessels and blood) and other systems, such as the lungs, for oxygen. No level is “most important”; each depends on the others. [3 marks: cells and tissues; system or other systems; conclusion]
Show What You Know
7. Marking guide: 1 position (plants are organised differently, not less); 2 comparing both at all four levels with examples (1 if two or three levels); 1 accepting the true facts (no heart, lungs or brain; many plants regrow from cuttings); 1 regrowing shows plant cells can build new tissues and organs, which is organisation, not a lack of it; 1 judgement that both are organised living systems. Model answer: Plants are organised differently, not less. A koala has muscle cells, muscle tissue, a heart and a circulatory system; a gum tree has leaf cells, photosynthetic tissue, leaves, and root and shoot systems. Regrowing from a cutting shows plant cells can build new tissues and organs. Both are organised living systems whose parts work together. [6 marks]
Common error to watch for: treating a heart, lungs or brain as proof of organisation.