7A Cells, Tissues, Organs and Systems
7E Mixtures and Separation
7G The Particle Model
7J Current Electricity
7L Sound
100
What part of a plant cell controls what enters and leaves the cell?
The cell surface membrane.
Explanation: It controls substances moving into and out of the cell.
100
What is the liquid in a solution called?
The solvent.
Explanation: The solvent is the liquid in which another substance dissolves.
100
What is diffusion?
The spreading out of particles.
Explanation: Particles move randomly and spread from areas of higher concentration towards areas of lower concentration.
100
What happens to a circuit when an open switch is closed?
Answer: Current can flow.
Explanation: Closing the switch completes the circuit.
100
What is the unit used to measure frequency?
Hertz (Hz)
200
Name TWO structures found in plant cells but not animal cells.
Any two of: cell wall, chloroplasts, vacuole.
Explanation: These are characteristic structures of plant cells.
200
What type of mixture is muddy water: a solution, colloid or suspension?
A suspension.
Explanation: It contains insoluble solid particles that can settle out if the mixture is left standing.
200
Why can a gas be compressed but a liquid cannot easily be compressed?
Gas particles have large spaces between them.
Explanation: These spaces can be reduced. Liquid particles are already close together, so there is very little space to remove.
200
In a series circuit, one bulb breaks. What happens to the other bulbs?
They all go out.
Explanation: A series circuit has only one path. A broken bulb creates a gap, so current cannot flow anywhere in the circuit.
200
A tuning fork vibrates 600 times every second. What is its frequency?
Answer: 600 Hz.
Explanation: One hertz means one vibration per second.
300
Put these in order from smallest to largest:
organ – cell – organ system – tissue
cell → tissue → organ → organ system
Explanation: Similar cells form tissues; tissues form organs; organs work together in organ systems.
300
20 g of sugar is completely dissolved in 150 g of tea. What is the total mass of the solution?
170 g.
Explanation: Mass is conserved:
150 g + 20 g = 170 g
300
What is the difference between a scientific hypothesis and a scientific theory?
A hypothesis is an idea that can be tested. A theory is supported by evidence from many experiments.
Explanation: A hypothesis may develop into a theory when repeated experimental evidence supports it.
300
Two identical bulbs are connected in series. A third identical bulb is added in series. What happens to the brightness of the bulbs?
Answer: They become dimmer.
Explanation: Adding another bulb increases the resistance, making it more difficult for current to flow. The current therefore decreases.
300
Put these parts of the ear in the correct order, starting when a sound wave enters the ear:
cochlea – ear bones – ear canal – eardrum
Answer:
ear canal → eardrum → ear bones → cochlea
Explanation: Sound travels down the ear canal, vibrates the eardrum, the ear bones amplify the vibrations, and the vibrations then enter the cochlea.
400
Explain why the heart is described as an organ rather than a tissue.
The heart contains different types of tissue working together to perform a function.
Explanation: A tissue consists of similar cells, whereas an organ contains several tissues. The book shows muscle, nerve and fat tissues in the heart.
400
A student heats salt water until all the water has evaporated. Another student uses distillation. Explain the important difference between what the two students can collect.
With evaporation, the student can collect the salt. With distillation, the student can also collect the water.
Explanation: In distillation, the evaporated water is cooled so that it condenses back into liquid water and can be collected.
400
A student pushes down the plunger of a sealed syringe containing air. Explain what happens to the density AND pressure of the gas.
Both the density and pressure increase.
Explanation: The same number of particles is squeezed into a smaller volume. The particles therefore hit the syringe walls more frequently, increasing pressure.
400
Why is a parallel circuit more suitable than a series circuit for lights in a house?
Answer: Appliances can operate independently, and one breaking does not turn all the others off.
Explanation: Each appliance has its own branch, so current can still flow through the other branches.
400
A dolphin sends out an ultrasound pulse and detects an echo. How can it use the echo to determine how far away an object is?
Answer: It measures the time between sending the sound and receiving the echo.
Explanation: The longer the echo takes to return, the further away the object is.
500
A plant's roots are healthy and absorbing plenty of water, but its xylem tissue becomes badly damaged. Predict what could happen to the leaves and explain why.
The leaves could wilt and eventually die because insufficient water would reach them.
Explanation: Roots absorb water, but xylem transports that water from the roots to the rest of the plant. Healthy roots alone are therefore not enough if the transport tissue is damaged.
500
A mixture contains water, dissolved salt and insoluble sand. Describe how you could separate the mixture to obtain BOTH the sand and the salt.
First filter the mixture, then evaporate the filtrate.
Explanation:
Filtration traps the sand as residue while the salt solution passes through. Evaporating the water from the filtrate then leaves the salt behind.
500
Two identical balloons contain the same gas. Balloon A contains more gas particles than Balloon B, but both balloons are the same size. Which balloon should have the greater pressure? Explain using particle theory.
Balloon A.
Explanation: More particles occupy the same volume, so there will be more collisions with the balloon walls. This produces greater gas pressure.
500
An electrical appliance normally takes a current of 6 A. You can choose a 3 A, 5 A, 10 A or 13 A fuse. Which should you choose and why?
Answer: The 10 A fuse.
Explanation: The fuse must allow the normal 6 A current to flow, so 3 A and 5 A are too small. The smallest suitable rating above the normal current is 10 A, providing better protection than 13 A.
500
Astronauts outside a spacecraft cannot hear each other speaking normally, but they could hear each other if their helmets were touching. Explain both observations.
Answer: Space is effectively a vacuum, so normal speech cannot travel between the astronauts. If their helmets touch, vibrations can travel through the solid material of the helmets.
Explanation: Sound requires particles to transfer vibrations. There are essentially no particles between them in space, but there are particles in the solid helmets.