A Level Biology AQA

This subject is broken down into 94 topics in 10 modules:

  1. Handling data 13 topics
  2. Biological Molecules 10 topics
  3. Cells 12 topics
  4. Exchange and Transport Systems 10 topics
  5. Genetic Information, Variation, and Relationships Between Organisms 9 topics
  6. Energy Transfers In and Between Organisms 8 topics
  7. Organism Changes in their Environments 11 topics
  8. Genetics, Populations, Evolution, and Ecoosystems 10 topics
  9. The Control of Gene Expression 6 topics
  10. Using Genome Projects 5 topics
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  • 94
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This page was last modified on 28 September 2024.

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Biology

Handling data

Planning Investigations: Hypothesis Formation

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Planning Investigations: Hypothesis Formation

Formation of Hypothesis

  • A hypothesis is a clear, concise, and testable statement that expresses the expected outcome or prediction for a scientific investigation.
  • An effective hypothesis should be based on prior knowledge or observation.
  • Hypotheses are often stated as an “If…, then…” statement that predicts the effect of one variable on another.
  • The independent variable is the factor that is manipulated or changed during an experiment, while the dependent variable is the factor that is measured.
  • Hypothesis should express a cause and effect relationship between the independent and dependent variables.
  • The hypothesis is not the end result; rather, it guides the data collection and analysis phase of the research project.

Characteristics of a Valid Hypothesis

  • It must be a testable statement—one that can give rise to measurable outcomes.
  • It should identify and relate the independent and dependent variables clearly.
  • It needs to be based on existing scientific knowledge.
  • It should be simple and specific, using precise terminology.
  • A valid hypothesis often predicts the anticipated direction of the effect.

Importance of Null Hypothesis

  • The null hypothesis (H0) states that there is no relationship or effect of the independent variable on the dependent variable in the investigated population.
  • It represents a statement of no difference or no association between variables and serves as the basis of comparison for testing the alternative hypothesis.
  • The aim is not necessarily to prove the null hypothesis correct, but to determine whether it can be rejected or not rejected based on the evidence collected.

Alternative Hypothesis

  • The alternative hypothesis (H1 or Ha) is the rival claim to the null hypothesis that we believe might be true instead.
  • It proposes that there is a significant interaction or relationship between the variables studied.
  • It is evaluated based on the end results; if the results provide enough evidence against the null hypothesis, the alternative hypothesis is deemed more likely.

Course material for Biology, module Handling data, topic Planning Investigations: Hypothesis Formation

Biology

Genetic Information, Variation, and Relationships Between Organisms

The Chromosome Content of Cells After the First and Second Meiotic Division

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The Chromosome Content of Cells After the First and Second Meiotic Division

The Chromosome Content of Cells After the First Meiotic Division

  • Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell. Meiosis includes two consecutive divisions: Meiosis I and II.
  • In Meiosis I, called the reductional division, chromosomes duplicate and homologous chromosomes pair, each consisting of two sister chromatids.
  • This pairing leads to crossing over or recombination, creating new combinations of genes which contribute to genetic variation.
  • After crossing over, there's segregation of homologous chromosomes into two daughter cells. Here each cell receives one complete set of chromosomes (haploid), but each chromosome still consists of two sister chromatids.
  • The number of chromosomes is halved in Meiosis I, and therefore the chromosome content in each of the two daughter cells is haploid.

The Chromosome Content of Cells After the Second Meiotic Division

  • Meiosis II, also known as the equational division, resembles mitosis but takes place in the absence of chromosome replication.
  • The sister chromatids of each chromosome from Meiosis I separate and move into separate daughter cells.
  • The process of Meiosis II yields four new cells, each containing a haploid number of chromatids.
  • At the end of Meiosis II, the four daughter cells have half the chromosome number of the original cell, and each chromosome consists of one chromatid.
  • As a result of recombination and individual assortment, the four daughter cells are genetically different from each other and the parent cell.

Understanding the Importance of Meiosis

  • The division process of Meiosis and the reduction in chromosome number is crucial for sexual reproduction. It allows for the combination of paternal and maternal genes while maintaining a consistent chromosome number across generations.
  • The daughter cells produced by meiosis are known as gametes or sex cells (sperm and eggs in animals).
  • The genetic variation in gametes, resulting from meiosis, contributes to the biodiversity of species and helps populations adapt to changing environments.
  • Errors in Meiosis can cause genetic disorders because of the abnormal number of chromosomes in the gametes, these conditions are called aneuploidies, for example, Down Syndrome, Klinefelter Syndrome and Turner Syndrome.

Course material for Biology, module Genetic Information, Variation, and Relationships Between Organisms, topic The Chromosome Content of Cells After the First and Second Meiotic Division

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