What are the solutions to the following questions? 1(a) Classify organisms into kingdoms. 1(b) List three plant cell structures. 2(i) Name molecules NF3, SO3, SiF4. 2(ii) Name atom particles, their ma

Let $V$ be the total volume of the plank, and $\rho_w$ be the density of water.
When floating, the buoyant force equals the weight of the plank.

$$\text{Weight of plank} = \text{Weight of water displaced}$$ $$\rho_p V g = \rho_w \left(\frac{2}{3}V\right) g$$ $$\rho_p = \frac{2}{3} \rho_w$$

Let $\rho_L$ be the density of the unknown liquid.

$$\text{Weight of plank} = \text{Weight of liquid displaced}$$ $$\rho_p V g = \rho_L \left(\frac{1}{2}V\right) g$$ $$\rho_p = \frac{1}{2} \rho_L$$

$$\frac{2}{3} \rho_w = \frac{1}{2} \rho_L$$ $$\rho_L = \frac{2}{3} \times 2 \rho_w$$ $$\rho_L = \frac{4}{3} \rho_w$$

Relative density of liquid $= \frac{\text{Density of liquid}}{\text{Density of water}}$

$$\text{Relative density} = \frac{\rho_L}{\rho_w} = \frac{\frac{4}{3} \rho_w}{\rho_w} = \boxed{\frac{4}{3} \text{ or } 1.33}$$

4 (i) Distinguish between a grain and a cereal.
A grain is a small, hard, dry seed, with or without an attached hull or fruit layer, harvested for human or animal consumption. A cereal is a type of grain that comes from grasses cultivated for their edible components, such as wheat, rice, or maize. All cereals are grains, but not all grains are cereals (e.g., legumes like lentils are grains but not cereals).

4 (ii) State one example of a grain.
Maize (Corn)

4 (iii) Mention four uses of the named grain in d (ii). [5 marks]
(Assuming "d (ii)" refers to "4 (ii)", and the named grain is Maize)

• Food for human consumption (e.g., cornmeal, sweet corn, popcorn).
• Animal feed for livestock.
• Production of ethanol (biofuel).
• Source of corn oil and corn starch.

5 (i) Define the following terms

• (α) Mitosis: Mitosis is a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus. It is essential for growth, repair, and asexual reproduction.
• (β) Meiosis: Meiosis is a type of cell division that reduces the number of chromosomes in the parent cell by half and produces four haploid gamete cells. This process is crucial for sexual reproduction.

5 (ii) Mention two ways in which meiosis is significant. [6 marks]

• Meiosis ensures genetic variation in offspring through processes like crossing over and independent assortment of chromosomes, leading to diverse traits within a species.
• It maintains a constant chromosome number across generations in sexually reproducing organisms by halving the chromosome number in gametes, so that when two gametes fuse during fertilization, the diploid number is restored.

6 (i) (α) Explain the term isomers.
Isomers are compounds that have the same molecular formula but different structural formulas or different arrangements of atoms in space. This difference in arrangement leads to distinct chemical and physical properties.

6 (i) (β) Write down structures for three isomers of hexane. [6 marks]
Hexane has the molecular formula C$_6$H$_{14}$.

1. n-Hexane (straight chain)

   $$\text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_2\text{CH}_3$$

2. 2-Methylpentane

   $$\begin{matrix} & \text{CH}_3 \\ & | \\ \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}\text{CH}_3 \end{matrix}$$

3. 2,3-Dimethylbutane

   $$\begin{matrix} & \text{CH}_3 & \text{CH}_3 \\ & | & | \\ \text{CH}_3\text{CH}\text{CH}\text{CH}_3 \end{matrix}$$