Life Science Grade 11 | Term 1 Revision 2

Study the diagrams below of micro-organisms and answer the questions that follow

Question

Name the group of organisms to which B and C belong respectively.

Organism B belongs to the group of viruses. Viruses are microscopic infectious agents that can only replicate inside a living host cell. They are not considered fully living organisms because they lack cellular structure and cannot carry out metabolic processes independently.

Organism C belongs to the group of fungi. Fungi are eukaryotic organisms that include molds, yeasts, and mushrooms. They reproduce using spores and obtain nutrients through decomposition or symbiotic relationships.

Question

Provide labels for:

(a) 1 – Flagellum
The flagellum is a whip-like structure that enables movement in certain microorganisms, such as bacteria and some protists. It helps the organism navigate through its environment in response to stimuli.

(b) 2 – Nucleic acid / RNA / DNA
Nucleic acids, such as DNA or RNA, store genetic information. In viruses, either DNA or RNA is present, which enables them to hijack a host cell’s machinery to reproduce.

(c) 3 – Sporangium
A sporangium is a structure in fungi where spores are produced and stored. These spores are later released for reproduction and dispersal.

Question

Give the LETTER of the organism that:

(a) Is not considered to be living – B
Viruses (organism B) are not classified as living organisms because they lack cellular structures and cannot reproduce independently. They require a host cell to multiply.

(b) Is eukaryotic – C
Fungi (organism C) are eukaryotic because they have membrane-bound organelles, including a nucleus containing their genetic material.

Question

Name the shape of the bacterium in Diagram A.

The bacterium in Diagram A is bacillus / rod-shaped. Bacilli are cylindrical bacteria that can exist as single cells or in chains. Their elongated shape allows efficient absorption of nutrients and movement in liquid environments.

Study the micrograph and answer the questions

Question 5.1

Identify the parts labelled A – E.

The structure labelled A is the rhizoid/hyphae. Rhizoids are root-like structures that anchor the fungus to a substrate and aid in nutrient absorption. Hyphae are the filamentous structures that make up the body of a fungus, playing a crucial role in growth and reproduction.

The structure labelled B is the sporangiophore. A sporangiophore is a specialized hyphal structure that supports the sporangium, elevating it to enhance the dispersal of spores.

The structure labelled C is the spore. Spores are reproductive units that allow fungi to propagate and spread under favorable conditions. They are resistant to environmental stresses and play a key role in the fungal life cycle.

The structure labelled D is the columella. The columella is an internal structure within the sporangium that provides support and distributes nutrients to developing spores.

The structure labelled E is the septum. A septum is a partition that divides fungal hyphae into individual cells or compartments, controlling the flow of cytoplasm and organelles between sections.

Question

Use the scale line to calculate the length of the structure labelled C.

The measured length of C is 2.5 mm.

The scale provided in the micrograph shows that 18 mm corresponds to 60 µm.

To calculate the actual length of C, the formula used is:

Actual Length = (Measured Length × Scale Value) ÷ Scale Length

Substituting the values:

Actual Length = (2.5 × 60) ÷ 18

Actual Length = 8.3 µm

Thus, the actual length of the structure labelled C is 8.3 µm.

Question 4.1

Name the form of nitrogen which higher plants use.

Higher plants primarily absorb nitrates from the soil. Nitrates are essential for plant growth as they are a key component of amino acids, proteins, and chlorophyll, which are necessary for photosynthesis and overall plant development.

Question

Describe THREE ways in which nitrogen becomes available to higher plants.

Nitrogen becomes available to higher plants through several natural processes:

• Lightning converts atmospheric nitrogen and oxygen into nitrates. When lightning strikes, the high energy causes nitrogen molecules to react with oxygen, forming nitrogen oxides. These dissolve in rainwater and enter the soil as nitrates, which plants can absorb.
• Free-living soil bacteria can form nitrates. Certain bacteria in the soil, such as nitrifying bacteria, convert atmospheric nitrogen into ammonia and subsequently into nitrates, making nitrogen accessible to plants.
• Root nodule bacteria contribute to nitrogen availability. Leguminous plants host nitrogen-fixing bacteria, such as Rhizobium, in their root nodules. These bacteria convert atmospheric nitrogen into ammonium compounds, which are further converted into nitrates for plant absorption.

Question

Briefly describe the ecological role of algae:

a) As Producers in Ecosystems

Algae are primary producers in marine and freshwater ecosystems, meaning they are the first source of food in the food chain. They contain chlorophyll, which allows them to perform photosynthesis—a process where they use sunlight to make their own food. This food is then passed on to herbivores and other animals, providing energy for the entire ecosystem. Without algae, many aquatic organisms would not have a food source.

(b) In the Maintenance of Oxygen-Carbon Dioxide Balance

Algae help to maintain the balance of oxygen and carbon dioxide in the environment. During photosynthesis, they absorb carbon dioxide from the air and water and use it to make food. At the same time, they release oxygen as a byproduct, which is essential for the survival of animals and other organisms that rely on oxygen for respiration. This process ensures that oxygen levels remain stable in the atmosphere and water.

Read and answer the questions which follow.
A type of bacterium called Escherichia coli (E. coli) normally lives in the large intestine of humans. To determine whether E. coli is present in water, a chemical indicator is used. If the chemical indicator changes from a clear red colour to a cloudy yellow colour, it confirms the presence of E. coli.

A group of Grade 11 learners conducted an investigation to test for E. coli in water samples collected from three rivers: X, Y, and Z. The water samples were placed in glass bottles containing the clear red indicator solution. These bottles were then incubated at 37°C for two days. After the incubation period, it was observed that only river Y showed the presence of E. coli, as indicated by the colour change of the indicator solution.

Question
Explain two safety precautions that the learners should take when conducting this investigation.

1, The learners should wear rubber gloves to avoid contamination when handling water samples. This is important because E. coli is a harmful bacterium that can cause infections if it comes into contact with open wounds or is accidentally ingested. Gloves also prevent contamination of the water samples, ensuring accurate results.

2, Additionally, sample bottles should be attached to a string to prevent them from slipping and falling into the river. This precaution reduces the risk of drowning, injuries, or further contamination of the river by disturbed sediments or broken glass bottles.

Question
Suggest one reason for incubating the sample at 37°C.

The samples were incubated at 37°C because this is the normal human body temperature, which is the environment where E. coli bacteria naturally live. Keeping the samples at this temperature ensures that any E. coli present can grow and be detected, making the test more reliable.

Question
State how E. coli could have entered river Y.

1, E. coli could have entered river Y due to a lack or absence of a proper sewage system. If human waste is not properly managed, it can leak into water sources, introducing harmful bacteria.

2, Another possible reason is that human faeces contaminated the water. This can happen when sewage overflows, improper waste disposal occurs, or people use the river for bathing or defecation, leading to E. coli contamination.