Cells and Photosynthesis
Both plant and animal cells contain mitochondria. Why?
Because both need to carry out aerobic respiration to release energy.
What does the word unicellular mean?
An organism made of one cell.
In an investigation, what is the name of the variable that you deliberately change?
The independent variable.
Which specialised cell carries oxygen around the body?
Red blood cell
Ecuador has four main geographical regions. Which one is located east of the Andes?
The Amazon region / Oriente
A student says: “If a cell has a cell wall, it must be a plant cell.” Why is this conclusion incomplete?
Because bacterial cells can also have cell walls. More evidence is needed to identify the cell.
Which unicellular organism contains circular DNA but does not have a nucleus?
A bacterium
When carrying a microscope across the laboratory, what is the safest method?
Carry it with two hands, one holding the arm and one supporting the base.
Why does a sperm cell have a flagellum?
To allow it to swim towards the egg cell.
Why can Quito have a relatively cool climate even though Ecuador lies on the Equator?
Because Quito is located at a high altitude in the Andes. Temperature generally decreases with altitude.
Two cells contain nuclei, cytoplasm and mitochondria. Cell A also contains many chloroplasts, while Cell B contains none. Cell A was taken from a leaf and Cell B from a root. Explain why this difference makes biological sense.
Leaf cells receive light and carry out photosynthesis, so they need chloroplasts. Root cells are usually underground and receive little or no light, so chloroplasts are generally not needed.
A euglena detects light and then swims towards it. Name the two structures mainly responsible.
Eyespot detects light; flagellum provides movement.
A student wants to observe a slide. Why should they begin with the lowest-power objective lens?
It gives a wider field of view and makes the specimen easier to locate and focus safely.
A root hair cell has a long extension. How does this help the plant?
It increases surface area, allowing more efficient absorption of water and mineral ions.
The Galápagos Islands are volcanic. What geological process explains how many of the islands were formed?
Volcanic activity, caused by magma rising through the crust over a hotspot.
Pondweed is moved closer and closer to a lamp. At first, the number of oxygen bubbles per minute increases, but eventually it stops increasing. Why?
Light was initially limiting photosynthesis, but eventually another factor becomes limiting, such as carbon dioxide.
An amoeba loses the ability to form food vacuoles but its contractile vacuole still works. Predict one problem the amoeba would eventually face.
It would have difficulty taking in/digesting food and would eventually lack the materials or energy needed for survival.
Students investigate whether light intensity affects photosynthesis. They change the distance between a lamp and pondweed and count bubbles produced per minute. Identify: IV, DV and one CV
Cigarette smoke damages the cilia in cells lining the airway. Why could this increase the chance of respiratory problems?
Damaged cilia cannot move mucus effectively. Mucus containing dust and microorganisms can accumulate, increasing the risk of irritation and infection.
Ecuador contains coastal areas, high mountains, Amazon rainforest and isolated islands. Explain one reason why this geographical variety can lead to high biodiversity.
Different regions provide different climates, habitats and environmental conditions, so different organisms can become adapted to different niches.
Two identical plants receive the same water, minerals and temperature. Plant A receives plenty of light. Plant B receives very little light. After several weeks, Plant A has grown much more. Explain the complete biological chain from light to growth.
More light
→ higher rate of photosynthesis
→ more glucose produced
→ more glucose available for respiration and making new materials
→ more energy/material available for growth.
A unicellular organism becomes much larger without changing its basic shape. Explain why relying only on diffusion may become less effective.
As the organism becomes larger:
A student prepares a microscope slide using a thin piece of plant tissue and a glass coverslip. Identify one hazard, the risk, and a suitable control measure.
Example:
A normal red blood cell has a biconcave shape. Imagine it becomes thick and spherical but keeps approximately the same volume. Predict how this could affect oxygen exchange.
Oxygen exchange would likely become less efficient because the cell would have a smaller surface area relative to its volume and a greater diffusion distance.
A species of bird is found both on mainland Ecuador and on an isolated Galápagos island. After many generations, the island population develops different beak shapes and feeding behaviours. Suggest why the two populations may become increasingly different over time.
Geographic isolation means the populations experience different environments and selection pressures. Different adaptations may become more common over generations, leading to greater differences between the populations.