OCR GCSE Biology B (Twenty First Century)
OCR GCSE Biology B B4.3 How do organisms grow and develop? Exam Questions
Free OCR GCSE Biology B exam questions for B4.3 How do organisms grow and develop?, with a mark scheme for every pack. Covers the cell cycle, mitosis, cell division, differentiation, specialised cells, stem cells, meristems and growth in plants and animals.
B4.3 How do organisms grow and develop? exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About OCR GCSE Biology B B4.3 How do organisms grow and develop?
B4.3 explains how a single fertilised egg grows into a complex multicellular organism. You need to describe the cell cycle, including DNA replication and mitosis, and explain how cells become specialised through differentiation. Differences between growth in plants and animals are important: plants keep meristems that can differentiate throughout life, whereas most animal cells differentiate early. This connects the genome in B1.1 with plant hormones in B4.4 and stem cells in B4.5. Examiners often ask you to sequence the stages of the cell cycle or to calculate the proportion of cells in mitosis from a root tip count.
What you need to know
- The cell cycle Before division the cell grows, makes more organelles such as mitochondria and ribosomes, and copies its DNA so each chromosome has two identical copies.
- Mitosis Chromosomes line up at the centre of the cell and the copies are pulled to opposite ends. The cytoplasm and membrane divide to form two genetically identical daughter cells.
- Uses of mitosis Mitosis is used for growth, repair of damaged tissue and asexual reproduction.
- Differentiation Differentiation is when a cell becomes specialised by switching on some genes and switching off others, so it develops the structures needed for its function.
- Stem cells Stem cells are undifferentiated cells that can divide and become specialised. Embryonic stem cells can form any cell type; adult stem cells, for example in bone marrow, form a limited range.
- Plant growth Meristems at shoot and root tips divide by mitosis throughout the plant's life, and their cells can differentiate into any plant tissue. Plant cells also grow by elongation.
Common mistakes in B4.3 How do organisms grow and develop?
- Saying the DNA divides into two during mitosis. DNA is copied before mitosis so each new cell gets a full set.
- Writing that mitosis produces gametes. Mitosis produces identical body cells; meiosis produces gametes.
- Stating that differentiated cells lose genes. They contain the same genes but only some are expressed.
- Claiming animals and plants grow in the same way. Plants retain meristems and grow by elongation; animals grow mainly by cell division.
- Forgetting that the cell grows and makes organelles before dividing. Include this stage when describing the cell cycle.
Try three B4.3 How do organisms grow and develop? exam-style questions
1. State one function of mitosis in animals. (1 mark)
Show the mark scheme answer
Growth; or repair of tissues.
2. In a root tip, 36 out of 300 cells were seen in mitosis. Calculate the percentage of cells in mitosis. (2 marks)
Show the mark scheme answer
36 / 300 x 100; = 12%.
3. Describe what happens during the cell cycle in a body cell. (4 marks)
Show the mark scheme answer
The cell grows and makes more organelles such as mitochondria; DNA is replicated so each chromosome is copied; in mitosis copies of each chromosome are pulled to opposite ends of the cell; the cytoplasm divides to form two genetically identical cells.
B4.3 How do organisms grow and develop? FAQs
What does OCR GCSE Biology B B4.3 cover?
It covers the cell cycle and mitosis, differentiation and specialised cells, stem cells and the differences between plant and animal growth.
Which paper is B4.3 examined in?
J257 has two papers at each tier, Breadth in Biology and Depth in Biology, and content from any chapter, including B4, can be assessed on either one. Expect it to be linked to ideas about science and to other chapters.
How can I remember the stages of the cell cycle?
Think grow, copy, separate, split: the cell grows and makes organelles, copies its DNA, separates chromosomes in mitosis, then splits the cytoplasm.
