Explain egg energy stores and the changing jelly coat
Original egg model: cytoplasmic energy stores support early development; the jelly coat changes at fertilisation to help restrict additional sperm entry.
Exam scope and assessment notes
Core and Extended · Biology 0970, 2026–2028. Use the stated specimen features and evidence. Diagrams are schematic. Written practice is self-checked; human subject-teacher review, supervised practical competence and cumulative assessment remain pending. Cambridge states that IGCSE 0970 has the same subject content as IGCSE 0610, with 9–1 grading. This StudyForA pathway maps the 2026–2028 syllabus only. This 9–1 graded qualification is available only in a limited number of administrative zones. Confirm that your centre can enter you for this code and exam series with Cambridge International. Cambridge has published a separate syllabus for 2029. StudyForA has not reconciled that version yet; this page supports exams in 2026, 2027 and 2028 only.
Before you begin
- Recall cell nuclei, gametes, diffusion, respiration and the difference between a cell and an organ.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is the main role of egg energy stores here?
What you will learn
- Locate the two required egg adaptations
- Link stored energy and coat change with early development
Original teaching model.
| Feature | Meaning |
|---|---|
| Energy stores | Resources for early development |
| Jelly coat | Changes at fertilisation |
| Change function | Helps prevent further sperm entry |
| Nucleus | Female nuclear contribution |
Locate the two required egg adaptations
The egg-cell model shows a large cytoplasm containing energy stores, a nucleus and an outer jelly coat. The separate sperm and egg drawings are enlarged independently and are not a shared scale comparison. The syllabus calls the surrounding protective layer a jelly coat; the model uses this term without requiring a detailed molecular description of its composition.
Energy stores in the egg support early development after fertilisation, before the developing embryo has established later placental support. They are resources, not energy created from nothing and not a substitute for the sperm nucleus. Link the store with the needs of early cells rather than claiming the egg has enough reserves to nourish an entire pregnancy by itself.
Link stored energy and coat change with early development
The jelly coat changes at fertilisation, helping prevent entry of additional sperm. That helps avoid multiple male nuclear contributions to the same egg. The coat does not become another embryo, supply the male nucleus or pull a sperm through the uterus. Its changing barrier role is different from the egg cytoplasm’s reserve role.
In an adaptation answer, give both structure–function links: stores support early development; coat change helps prevent further sperm entry. Do not promise that a cartoon coat proves every biological barrier always works or that a shown sperm has fused with the egg nucleus. These are conceptual explanations; actual events need evidence rather than an assumed outcome from an illustration.
Pause and explain
What is the coat-change role?
Worked example
Why is “the egg’s stores feed the whole fetus throughout pregnancy” too broad?
Show the worked solution
- Identify the early-development role.
- Distinguish later placental nutrient supply.
Answer Egg stores support early development; later fetal supply depends on placental exchange and the umbilical route, not the initial stores alone.
Try a topic test
Choose Easy, Normal or Difficult. Save your answers and open worked review after finishing.
Test this topic →From guided practice to a new situation
Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain the egg’s two required adaptive features.
Give me a hint
Connect reserves and barrier change separately.
Compare my reasoning
- State the early-development reserve role.
- State the further-entry restriction.
Energy stores support early development; the jelly coat changes at fertilisation, helping prevent additional sperm entering.
Look for these in your work
- Include both features
- Give two different functions
Correct “the jelly coat supplies the male nucleus and the cytoplasm blocks every sperm”.
Give me a hint
Assign nuclear contribution, reserves and coat change correctly.
Compare my reasoning
- Recall the sperm nuclear contribution.
- Match egg cytoplasm and coat with their roles.
The sperm supplies the male nucleus. Egg cytoplasm contains energy stores; its jelly coat changes at fertilisation to help prevent further sperm entry.
Look for these in your work
- Correct nuclear origin
- Separate stores and coat roles
A model shows an egg’s reserves and coat but no fertilisation record. Which adaptations can be identified and which event remains unproven?
Give me a hint
Visible features are not the same as an observed change.
Compare my reasoning
- Identify reserves and surrounding layer.
- Require evidence for fusion and later coat change.
Reserves and jelly coat can be identified; nuclear fusion and fertilisation-related coat change are not established by the static drawing alone.
Look for these in your work
- Identify the features
- Keep event claims bounded
Common mistakes
- The coat is not the egg nucleus.
- Egg reserves are not the complete pregnancy nutrient supply.
What can you explain now?
What is the coat-change role?
Compare with the explanation
Helping prevent additional sperm entry
The change supports restriction of further entry.
After trying it yourself, choose your next review. This is your self-assessment.
Your review choice appears on Today. Sign in to sync it across devices.
Make it stick
Explain locate the two required egg adaptations and link stored energy and coat change with early development. Use the diagram key and check your reasoning before opening the solutions.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.