Look inside the OCR A-Level Biology B (Advancing Biology) guide (H422)

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OCR · A-Level · H422
Biology B
Active Recall Guide
2,895 questions
Biology BContents
Contents
35 topics, 189 subtopics
  1. The Developing Cell: Cell Division and Cell Differentiation47
  2. The Developing Individual: Meiosis, Growth and Development80
  3. The Development of Species: Evolution and Classification87
  4. Cells and Microscopy170
  5. Water and Its Importance in Plants and Animals86
  6. Proteins and Enzymes99
  7. Nucleic Acids71
  8. Patterns of Inheritance78
  9. Population Genetics and Epigenetics59
  10. Gene Technologies81
  11. The Principles and Importance of Homeostasis54
  12. The Hormonal Control of Blood Glucose and the Management of Diabetes64
  13. and 23 more
ii
The Developing Individual: Meiosis, Growth and DevelopmentQuestions
The Developing Individual: Meiosis, Growth and Development
Meiosis, haploid gametes and genetic variation
  1. Define meiosis.
  2. What is meant by a haploid cell?
  3. What is a homologous pair of chromosomes?
  4. State the number of chromosomes in a human gamete and in a human zygote.
  5. Explain why meiosis is essential if the chromosome number is to stay the same from one generation to the next.
  6. In which organs does meiosis take place in humans?
  7. How does the outcome of meiosis in a human female differ from that in a human male?
  8. Where does meiosis occur in a flowering plant?
  9. Define fertilisation.
12
The Developing Individual: Meiosis, Growth and DevelopmentAnswers
Answers
Meiosis, haploid gametes and genetic variation
  1. Meiosis is a form of nuclear division in which one diploid cell gives rise to four haploid nuclei, each with half the chromosome number of the parent cell.
  2. A haploid cell contains a single set of chromosomes, one of each homologous pair, and is written as n.
  3. A homologous pair is two chromosomes of the same size carrying the same genes at the same loci, one inherited from each parent, though the alleles they carry may differ.
  4. A human gamete has 23 chromosomes and a human zygote has 46.
  5. Fertilisation combines two nuclei and so doubles the chromosome number, and meiosis halves it beforehand, so the zygote receives the normal diploid number rather than twice it.
  6. It takes place in the seminiferous tubules of the testes in males and in the ovaries in females.
  7. In the female the cytoplasm divides unequally, so one large functional egg cell is produced together with small polar bodies that degenerate, whereas in the male all four products mature into functional sperm.
  8. It occurs in the anthers, where it leads to the formation of pollen grains, and in the ovules, where it leads to the female gamete.
  9. Fertilisation is the fusion of the nuclei of a male and a female haploid gamete to form a diploid zygote.
13
Respiratory Diseases and TreatmentQuestions
Respiratory Diseases and Treatment
COPD, asthma and lung cancer
  1. Describe the changes to the airways that occur in chronic bronchitis.
  2. State two symptoms of chronic bronchitis.
  3. Why do people with chronic bronchitis suffer repeated chest infections?
  4. Describe the change to the alveoli that occurs in emphysema.
  5. Explain how tobacco smoke leads to the destruction of elastin in the alveoli.
  6. Explain why a person with emphysema becomes severely breathless.
  7. What does the term COPD stand for, and which two conditions does it usually describe together?
  8. Why is the airflow obstruction in COPD described as irreversible?
  9. Describe what happens in the airways during an asthma attack.
34
Respiratory Diseases and TreatmentAnswers
Answers
COPD, asthma and lung cancer
  1. The bronchi and bronchioles become chronically inflamed and swollen, the goblet cells and mucous glands enlarge and secrete excess mucus, and the cilia are destroyed so the mucus cannot be cleared.
  2. A persistent cough producing large amounts of sputum, and breathlessness caused by the narrowed, mucus-filled airways.
  3. Mucus that cannot be swept away by cilia pools in the airways and provides a warm, nutrient-rich place for bacteria to multiply.
  4. The elastin in the alveolar walls is broken down, so the walls between neighbouring alveoli break down and they merge into a few large air spaces.
  5. Smoke attracts phagocytes into the lungs, and these release the enzyme elastase, which digests the elastin of the alveolar walls.
  6. The merging of alveoli greatly reduces the surface area for gas exchange, and the loss of elastin means the lungs cannot recoil to force air out, so stale air is trapped and less fresh air is drawn in.
  7. COPD stands for chronic obstructive pulmonary disease, and it usually describes chronic bronchitis and emphysema occurring together.
  8. The destruction of elastin and the scarring of the airways are permanent structural changes, so no drug can restore the lost alveolar walls or cilia.
  9. The smooth muscle of the bronchioles contracts, the lining swells with fluid and extra mucus is secreted, so the lumen of each bronchiole is severely narrowed.
35
The Effects of Ageing on the Reproductive SystemQuestions
The Effects of Ageing on the Reproductive System
Ageing and the female reproductive system
  1. Describe how the number of oocytes in the ovaries changes over a woman's lifetime.
  2. Why does the quality of oocytes fall as a woman ages?
  3. At what age does a woman's fertility begin to decline, and why does the decline steepen later?
  4. State two consequences of increased non-disjunction in older oocytes.
  5. Why does blood FSH concentration rise as a woman approaches the menopause?
  6. Why is a raised FSH concentration useful as an indicator of approaching menopause?
  7. Define the menopause.
  8. What is the average age of the menopause in the UK?
  9. What is the perimenopause?
56
The Effects of Ageing on the Reproductive SystemAnswers
Answers
Ageing and the female reproductive system
  1. All the primary oocytes, around one to two million, are present before birth, and the number falls continuously from then on, so only a few hundred are ever ovulated and almost none remain by the menopause.
  2. Primary oocytes remain arrested in prophase I for decades, and the longer they are held there the more likely it is that the spindle fails to separate the homologous chromosomes correctly when meiosis I finally completes.
  3. It begins to decline from the early thirties and falls steeply after about 37, because the number of follicles remaining and the proportion of oocytes able to divide without chromosome errors are both falling at once.
  4. There is a higher chance of an embryo with an abnormal chromosome number, such as trisomy 21, and a higher chance of early miscarriage.
  5. Fewer follicles remain to be recruited, so less oestrogen and less inhibin are secreted, the negative feedback on the anterior pituitary weakens and more FSH is released.
  6. It reflects the size of the remaining follicle pool directly, so it rises before periods stop and gives a measurable sign of declining ovarian function.
  7. It is the permanent end of menstruation, diagnosed once twelve consecutive months have passed with no period.
  8. It is about 51 years.
  9. It is the transitional period of several years before the menopause during which hormone concentrations fluctuate widely, cycles become irregular and many of them are anovulatory.
57
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