Diagram 1 shows the process in the synthesis and secretion of extracellular enzymes in an animal cell.
a) Based on Diagram 1:
i) Explain the role of nucleus in the synthesis of enzyme. [ 3 marks]
Roles of nucleus in synthesis of enzyme are:
- it contains the cell’s hereditary information that is DNA in nucleolus
- it manufactures of subunits of ribosomes (RNA) and proteins associated with ribosome the important structures in the synthesis of proteins
- it has nuclear envelope with pores that allows ribosomal subunits to be exported to the cytoplasm where finally assembly of ribosomes takes place.
ii) Name one extracellular enzymes and describe how the different cellular components are involved in the secretion of this enzyme. [10 marks]
Digestive enzyme that is made by pancreas cell such as lipase is a type of extracellular enzyme.
- The instruction for making the extracellular enzyme is transcribed from deoxyribonucleic acid (DNA) to ribonucleic acid (RNA) in the nucleus.
- The RNA then leaves the nucleus through the nuclear pore and attaches itself to the ribosome located on the endoplasmic reticulum.
- When the enzyme synthesis is completed, it is extruded into the interior of the endoplasmic reticulum.
- The enzyme is then encapsulated in a transport vesicle.
- The transport vesicle fuses with the Golgi apparatus, releasing the enzyme into the Golgi apparatus.
- In the Golgi apparatus, the enzyme is further modified before being packed in a secretory vesicle.
- The secretory vesicle transports the enzyme to the plasma membrane.
- The secretory vesicle membrane fuses with the plasma membrane and the enzyme is released outside the cell.
"In multicellular organisms, cell specialization allows for division among tissues, organs and systems to carry out their specific roles."
Using the information given, explain what will happen to a cell if particular cellular components are absent. [8 marks]
Every cellular component works together for the survival and specific function of the cell. For example in nervous system, nerve cells are adapted for the transmission and reception of nerve impulses. Thus nerve cells requires more energy generated by mitochondria to carry out their functions.
If there is absence of mitochondria, no energy will produce. As a result nerve cells fail to carry out their functions. Similarly, in green plants, mesophyll cells in the leaves have chloroplasts to perform photosynthesis. If chloroplast is absent, light energy cannot be trapped for the purpose of photosynthesis.
Epithelial tissues that lining the inner wall of trachea consists of epithelial cells that have modified with the structure of goblet cells. These goblet cells secrete mucus to trap dust and particles in inhaled air.
A lot of Golgi apparatus with secretory vesicles are needed to secrete mucus. If there are no Golgi apparatus, no mucus will be secreted and the tissues cannot perform efficiently.
a) Figure 2(a) and 2(b) shows two different conditions of a plant before and after fertilizers are added within a week .
Describe the condition of plant in figure 2(a) before fertilizers are added. Explain how excess fertilizers affected this plant shown in figure 2(b)? If the plant in Figure 2(b) is watered immediately predict the changes that will occur in the plant cell.
Plant A has turgid cells because the cell saps of the plant cells are isotonic to the water in the soil. If too much fertilizer is added to the soil, the concentration of dissolved minerals is increases and water in the soil becomes hypertonic to the cell saps of the roots. Thus, water diffuses out of the cell to the soil by osmosis.
The cells become plasmolyses and the plant is wilted (Plant B). If this condition is prolonged the plant will die. But if the plant is watered immediately, it will turgid once again. This is because by watering the plant it will produce hypotonic condition of water in the soil to the cell saps. This will cause the water to diffuse into the cells by osmosis. The cells become deplasmolysed.
b) [10 marks]
"Mushrooms, mangoes and fish can be preserved longer using natural preservative such as sugar and salt. A housewife prefer to maintain the freshness of the mushrooms using suitable salt solution for a week. She also wanted to preserve the mangoes by using sugar solution and make salted fish by using salt."
i) Explain how the freshness of the mushroom can be maintained.
The mushroom is placed in a salt solution that is isotonic to the cell sap of the mushroom. There will be no net movement of water molecules. The mushroom cells maintain it turgidity. Hence, the freshness of the mushroom can be maintained.
ii) Describe how the principle of osmosis is applied when preserving mangoes using sugar solution and making salted fish by using salt.
The mangoes can be preserved by using sugar solution. The mangoes is places in a concentrated sugar solution that is hypertonic to the cell sap of mangoes. So water molecules diffuse from the mangoes into the surrounding hypertonic sugar solution by osmosis. This dehydrated condition is not suitable for the growth of bacteria. So, the mangoes is preserved.
Salted fish is made by using salt. When salt is applied on the surface of the fish’s skin, it will form a hypertonic condition. Water will diffuses from from the fish’s cells into the surrounding hypertonic saltsolution by osmosis. Water also diffuses from the cells of the bacteria found on the fish into the hypertonic salt solution. The bacterial cells are plasmolysed. Hence, the fish can be preserved.