Plant and animal cells

The prompt describes a cell with high energy requirements and mentions it has about 2000 mitochondria, so we should focus on what mitochondria provide when a cell needs lots of energy.

Mitochondria are often called the cell’s energy factories because they carry out aerobic cell respiration, releasing energy from nutrients and turning it into a form the cell can use quickly for work such as muscle contraction.

Now remove choices that are not the main output mitochondria make to satisfy energy needs:

• Oxygen and Glucose are materials needed for aerobic respiration. Mitochondria take these in and use them up; they are not the thing mitochondria are increasing to “supply” the cell.
• DNA does exist in mitochondria (mitochondrial DNA), but having many mitochondria is not mainly about providing DNA—it’s about meeting energy demand.

The key product made during aerobic respiration in mitochondria is ATP (Adenosine Triphosphate).

ATP is described as the cell’s “energy currency” because it delivers usable energy for processes like constant heart muscle contractions. Cells that work continuously need lots of ATP, which explains why heart muscle cells contain extremely large numbers of mitochondria.

To answer, remember the job of mitochondria. They’re known as the cell’s “powerhouse” because they are where aerobic cell respiration happens. Cells that must do lots of work all the time (like heart muscle cells) depend on a continuous stream of usable energy.

This links to Metabolism: Cell respiration and Cells: Cell structure in your syllabus.

Aerobic respiration requires reactants that get used up.

Oxygen and glucose are the main inputs. Because mitochondria use these rather than produce them as the final energy supply for the rest of the cell, these options can be eliminated.

Mitochondria do have their own DNA (mtDNA), which helps code for some mitochondrial proteins. But DNA is not what the cell is trying to “stock up on” for energy-demanding activity, so it is not the correct choice.

Mitochondria make ATP (adenosine triphosphate) during aerobic respiration. ATP stores energy in a form the cell can access immediately, such as to power heart muscle contractions.

Since the heart keeps beating continuously, cardiac cells need a huge, nonstop ATP supply, which is why they can have $2000+$ mitochondria.

In cells, what you see (structures) usually matches what the cell needs to do (its job). So we start by recalling the main function of a ribosome. Ribosomes are the cell parts that carry out protein synthesis. They read the instructions from genetic information and join amino acids together to form proteins the organism requires.

The cell described is specialized for hormone secretion. Many hormones (for example insulin and some growth hormones) are proteins. A cell that is dedicated to releasing these signals must manufacture large quantities of them. That means it needs lots of protein-building sites—ribosomes—to keep up with the high demand for making hormone molecules in bulk.

Now compare the answer choices with what ribosomes actually do:

• Option A matches vacuoles, which are used for storing water and wastes.
• Option B matches mitochondria, which release energy ($ATP$) for cell activities.
• Option C is about preventing bursting and maintaining structure, which relates to osmotic control and protective structures like the cell wall (in plants) or the cell membrane.

These functions don’t describe ribosomes, so they should be removed.

Because ribosomes are responsible for building proteins, a cell that produces lots of protein hormones will have many ribosomes compared with a typical skin cell. More ribosomes allow greater speed and volume of protein manufacturing.

First, recall what ribosomes do. They are the cell’s protein-making structures, often described as tiny “factories” for protein synthesis.

This is part of Cells: Cell structure. If the organelles are getting mixed up, reviewing the basic roles of the nucleus, mitochondria, vacuoles, and ribosomes can really help.

Option A talks about keeping extra water and waste. That storage role belongs mainly to the vacuole, not ribosomes. So this option can be eliminated.

Option B focuses on supplying energy for movement. Energy in the form of ATP is produced by the mitochondrion during cellular respiration. Ribosomes don’t make ATP, so this choice is incorrect.

Option C suggests preventing the cell from bursting. This is linked to structures and processes like the cell wall (in plants/bacteria), the cell membrane, and osmoregulation. Ribosomes are internal particles in the cytoplasm and don’t stop cells from bursting due to water movement.

Cells specialized for hormone secretion often release hormones that are proteins (peptide hormones). To secrete a lot of hormone, the cell must build a lot of protein quickly. Since ribosomes are where proteins are assembled, having many ribosomes directly supports the need for rapid, high-volume protein production.

The prompt describes a cell designed for the rapid transport of signals over long distances and points to a nerve cell (a neuron). To answer, we recall which neuron structure lets one cell connect far-apart body regions—like carrying a message from your back down to your toes.

This fits within Topic: Cells (Cell structure and Cell functions) in the MYP Biology course.

Now compare the choices. Neurons use lots of energy to keep ion differences across membranes and to recover after transmitting an impulse. If a neuron got rid of mitochondria, it would struggle to make enough ATP for active transport, so that option doesn’t match how neurons work.

A flagellum is mainly for motility—it helps the entire cell move through a liquid (for example, a sperm cell). Neurons usually stay positioned in tissues; they don’t travel around. Instead, they pass signals along their own cell structure, so a flagellum isn’t the key adaptation here.

Some cells do fuse into long, multinucleated cylinders—skeletal muscle fibers are the classic example. That design supports strong contraction. Neurons, however, remain separate cells and pass information across tiny gaps at synapses, rather than merging into one continuous tube for signaling.

A neuron has a cell body, dendrites that take in signals, and one very long extension called an axon.

The axon carries electrical impulses away from the cell body toward another neuron or an effector such as a muscle. Its great length is the main structural adaptation that makes fast communication over long distances possible.

Start by using the key clue: rapid transport of signals over long distances. In biology, form matches function, so we need a feature that lets a message travel from one region of the body to another efficiently without needing to hop repeatedly between many cells (which would slow things down).

A flagellum is a tail-like structure used for motility (moving the whole cell). That helps cells travel through fluid, but it doesn’t help an electrical signal move along the inside of a cell, so this choice can be ruled out.

Cells that fuse with others into a long cylindrical fiber are describing skeletal muscle. Even though those fibers are long, their structure is mainly for powerful contraction to move the skeleton, not for quickly sending electrical impulses across long distances in the body.

Losing mitochondria is something seen in mature red blood cells to free space for hemoglobin. Neurons, however, are highly active and need a steady ATP supply to maintain ion gradients and keep signaling. Without mitochondria, a neuron would not be able to function properly.

After eliminating the other choices, the best adaptation is having an axon. An axon is a single, extremely long extension of the cell that works like a biological ‘wire,’ allowing an electrical impulse (action potential) to travel from the cell body to a far-away target quickly—exactly what a nerve cell needs.

We need to match a cell part to three main hints:

1. It is mostly a water-based (aqueous) mixture.
2. It has nutrients and enzymes dissolved in it.
3. It’s where lots of the cell’s chemical reactions (metabolism) take place.

These clues point to the general internal fluid environment of the cell rather than a single small structure or pigment.

The cytoplasm is the semi-fluid material filling the inside of the cell. It includes the cytosol (the mostly-water liquid) with organelles suspended within it.

Because it is largely water, many substances can dissolve and move through it, and many enzyme-controlled reactions needed for life happen there.

Chlorophyll is a green molecule (pigment) located in chloroplasts. Its role is capturing light energy for photosynthesis, not serving as the cell’s general watery solution where most reactions occur.

Cell sap is the fluid inside the large permanent vacuole in plant cells. It can contain water and dissolved substances, but it mainly supports storage and helps keep the cell firm (turgor), rather than being the main place where general metabolism happens.

The nucleolus is a compact area within the nucleus. Its main job is making parts of ribosomes. It is not the widespread watery medium filling most of the cell.

Using the definition and eliminating the other choices, the description matches the cytoplasm, which is the aqueous environment where many metabolic reactions take place.

The correct answer must fit all parts of the description:

1. It must be an aqueous solution.
2. It must have enzymes and nutrients dissolved within it.
3. It must be a common location where metabolic reactions occur.

We can test each option and cross out the ones that don’t fit.

Chlorophyll is a pigment inside chloroplasts that absorbs light for photosynthesis. Even though photosynthesis is a metabolic process, chlorophyll itself is not the cell’s overall watery reaction medium.

Cell sap is found in plant cell vacuoles. It is water-based and may contain dissolved sugars and salts, but it is mainly for storage and maintaining internal pressure, not for being the primary site of general cellular metabolism.

The nucleolus is a specialized part inside the nucleus that builds and assembles ribosome components. It is not the broad, watery environment where many different metabolic pathways occur.

After eliminating the other choices, the best fit is the cytoplasm. The cytoplasm (especially the cytosol) is the jelly-like, water-based material filling the cell, holding organelles, containing enzymes for pathways such as glycolysis, and providing the setting for many chemical reactions.