Reactions of non-metals with oxygen - Grade 9 PDF Download

Table of Contents
1. Section A: Multiple Choice
2. Section B: True or False
3. Section C: Match the Column
4. Section D: Fill in the Blanks
5. Section E: Short Questions
6. Section F: Scenario Question
7. Section G: Long Question
8. Answer Key
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Section A: Multiple Choice

1. Which of the following best describes DNA?
   1. A carbohydrate that stores energy in cells
   2. A molecule that carries genetic information in living organisms
   3. A protein that controls chemical reactions in the body
   4. A lipid that forms the cell membrane
   [2]
2. Thandi observes that her eye colour is the same as her mother's. This is an example of:
   1. Adaptation
   2. Mutation
   3. Heredity
   4. Evolution
   [2]
3. Where in the cell is genetic material found?
   1. In the cytoplasm
   2. In the nucleus
   3. In the cell membrane
   4. In the mitochondria
   [2]
4. A gene can best be defined as:
   1. The complete set of chromosomes in an organism
   2. A section of DNA that codes for a specific trait
   3. The physical appearance of an organism
   4. A type of cell found only in plants
   [2]

Section B: True or False

1. All body cells in humans contain 46 chromosomes. [1]
2. Chromosomes are made of protein only. [1]
3. A child inherits half of their genetic information from each parent. [1]
4. Gametes (sex cells) contain the same number of chromosomes as body cells. [1]

Section C: Match the Column

Match each term in Column A with the correct description in Column B. Write only the letter of your answer.

[4]

Section D: Fill in the Blanks

Word Bank: alleles, dominant, recessive, phenotype

1. The physical appearance of an organism is called its ________. [1]
2. Different forms of the same gene are called ________. [1]
3. A ________ trait is expressed even when only one copy is present. [1]
4. A ________ trait is only expressed when two copies are present. [1]

Section E: Short Questions

1. Explain the difference between DNA and a chromosome. [3]
2. Why do offspring look similar to their parents? [2]
3. List two inherited traits and two acquired characteristics in humans. [4]
4. Sipho has brown eyes, but both his parents have blue eyes. Suggest why this might happen using your knowledge of genetics. [3]

Section F: Scenario Question

Lerato is studying her family tree for a school project. She notices that her grandmother, mother, and she all have a widow's peak (a V-shaped hairline), but her father and brother do not. Lerato learns that the widow's peak is a dominant trait.

1. What is a dominant trait? [2]
2. If the allele for widow's peak is represented by W and the allele for straight hairline by w, what possible genotypes could Lerato have? [2]
3. Explain why Lerato's brother does not have a widow's peak even though their mother does. [3]
4. If Lerato's genotype is Ww and she has children with someone who has genotype ww, what is the probability that their children will have a widow's peak? Show your working using a simple diagram or explanation. [4]

Section G: Long Question

Bongani investigates how traits are inherited in pea plants. He crosses a tall pea plant (TT) with a short pea plant (tt). The tall trait is dominant and the short trait is recessive.

1. What will be the genotype of all the offspring (F₁ generation) from this cross? Explain your answer. [3]
2. What will be the phenotype of all the F₁ generation plants? [2]
3. If Bongani now crosses two plants from the F₁ generation with each other, draw a Punnett square to show the possible genotypes of the F₂ generation. [4]
4. Using your Punnett square from question 3, calculate the ratio of tall to short plants expected in the F₂ generation. Explain whether this supports the principle of dominance. [4]

[Grand Total: 60]

Answer Key

Well done for completing the worksheet! Remember to always attempt all questions before checking your answers. Use this answer key to learn from any mistakes and strengthen your understanding of heredity and genetics.

Section A - Question 1

B - A molecule that carries genetic information in living organisms

DNA (deoxyribonucleic acid) is the molecule that stores all the genetic instructions needed to build and maintain a living organism. It is not a carbohydrate, protein, or lipid.

Section A - Question 2

C - Heredity

Heredity is the passing of traits from parents to their offspring through genetic information. Eye colour is inherited from parents, which is why Thandi's eyes are the same colour as her mother's.

Section A - Question 3

B - In the nucleus

The genetic material (DNA) is found in the nucleus of the cell, organized into chromosomes. The nucleus acts as the control center of the cell.

Section A - Question 4

B - A section of DNA that codes for a specific trait

A gene is a specific segment of DNA that contains the instructions for making a particular protein or controls a specific characteristic, such as eye colour or height.

Section B - Question 1

TRUE

Human body cells (somatic cells) contain 46 chromosomes arranged in 23 pairs. This is the normal chromosome number for humans.

Section B - Question 2

FALSE

Corrected statement: Chromosomes are made of DNA and protein.

Chromosomes consist of DNA wrapped around proteins called histones. They are not made of protein only.

Section B - Question 3

TRUE

Each parent contributes one set of 23 chromosomes through their gametes (egg or sperm), so a child receives half their genetic information from each parent.

Section B - Question 4

FALSE

Corrected statement: Gametes (sex cells) contain half the number of chromosomes as body cells.

Gametes contain only 23 chromosomes (haploid), while body cells contain 46 chromosomes (diploid). This ensures that when fertilization occurs, the offspring has the correct number of chromosomes.

Section C - Match the Column

• 1 - B: A chromosome is a thread-like structure made of DNA found in the nucleus. It carries genetic information.
• 2 - A: Heredity is the passing of traits from parents to offspring through genes.
• 3 - D: A trait is a characteristic (like eye colour or height) that can be inherited.
• 4 - C: Genotype refers to the genetic makeup (the combination of alleles) of an organism.

Section D - Question 1

phenotype

The phenotype is what you can observe or measure in an organism, such as its appearance, behaviour, or biochemical properties. It results from the interaction of the genotype with the environment.

Section D - Question 2

alleles

Alleles are different versions of the same gene. For example, there may be an allele for brown eyes and an allele for blue eyes.

Section D - Question 3

dominant

A dominant trait only needs one copy of the allele to be expressed in the phenotype. It "dominates" over the recessive allele.

Section D - Question 4

recessive

A recessive trait requires two copies of the allele (one from each parent) to be expressed. If a dominant allele is present, the recessive trait will not show.

Section E - Question 1

DNA is the chemical molecule that contains all the genetic instructions. A chromosome is a structure made when DNA is tightly coiled and packaged with proteins. Chromosomes are found in the nucleus and are visible during cell division, while DNA is the molecule itself.

• Definition of DNA [1]
• Definition of chromosome [1]
• Relationship between them [1]

Section E - Question 2

Offspring look similar to their parents because they inherit genetic information (DNA) from both parents. This genetic material contains genes that determine traits such as eye colour, hair texture, and height.

• Mention of inherited genetic information [1]
• Explanation that genes determine traits [1]

Section E - Question 3

Inherited traits: eye colour, hair colour, blood type, skin colour (any two)

Acquired characteristics: scars, language spoken, muscle development from exercise, learned skills (any two)

• Two inherited traits [2]
• Two acquired characteristics [2]

Section E - Question 4

This might happen because brown eyes are dominant and blue eyes are recessive. Both of Sipho's parents could be heterozygous (carrying one brown allele and one blue allele), so they have blue eyes. Sipho could have inherited the brown allele from both parents, giving him brown eyes.

• Mention of dominant/recessive [1]
• Explanation of parents being carriers [1]
• Explanation of inheritance [1]

Section F - Question 1

A dominant trait is a characteristic that is expressed in the phenotype even if only one copy of the dominant allele is present. It masks the effect of a recessive allele.

• Definition [1]
• Mention that only one copy is needed [1]

Section F - Question 2

Lerato could have the genotypes WW or Ww. Both genotypes will result in the widow's peak phenotype because W is dominant.

• WW [1]
• Ww [1]

Section F - Question 3

Lerato's brother does not have a widow's peak because he inherited two recessive alleles (ww) - one from each parent. Their mother must be heterozygous (Ww), carrying one dominant and one recessive allele. She passed the recessive allele (w) to her son, and he also received a recessive allele from his father.

• Brother has genotype ww [1]
• Mother is heterozygous [1]
• Explanation of inheritance [1]

Section F - Question 4

If Lerato is Ww and her partner is ww, the possible offspring genotypes are:

Lerato's alleles: W and w
Partner's alleles: w and w
Possible combinations:
• Ww (widow's peak)
• Ww (widow's peak)
• ww (straight hairline)
• ww (straight hairline)

The probability is 50% or 1 in 2 (or 2 out of 4) that their children will have a widow's peak.

• Correct identification of alleles [1]
• Showing combinations [2]
• Correct probability [1]

Section G - Question 1

All offspring in the F₁ generation will have the genotype Tt. This is because the tall parent (TT) can only give a T allele, and the short parent (tt) can only give a t allele. Every offspring receives one allele from each parent, resulting in Tt.

• Correct genotype Tt [1]
• Explanation of alleles from TT parent [1]
• Explanation of alleles from tt parent [1]

Section G - Question 2

All F₁ generation plants will be tall because they all have the genotype Tt, and the tall allele (T) is dominant over the short allele (t).

• Phenotype is tall [1]
• Explanation using dominance [1]

Section G - Question 3

Punnett Square for Tt × Tt:

Possible genotypes: TT, Tt, Tt, tt

• Correct setup of Punnett square [2]
• Correct genotypes in all four boxes [2]

Section G - Question 4

From the Punnett square, there are 3 tall plants (TT, Tt, Tt) and 1 short plant (tt). The ratio is 3:1 (tall to short).

This supports the principle of dominance because even though half of the F₂ plants carry the recessive allele (t), only those with two recessive alleles (tt) show the short phenotype. The presence of even one dominant allele (T) results in a tall plant, demonstrating that the dominant trait masks the recessive trait.

• Correct ratio 3:1 [1]
• Correct count from Punnett square [1]
• Explanation of dominance principle [1]
• Link to results [1]

Mark Allocation Summary

Keep up the excellent work! Review any questions you found challenging and make sure you understand the key concepts of heredity, DNA, chromosomes, genes, and inheritance patterns.