MYP Biology 1.2 Cell Functions Notes

So What's In a Cell?

Understanding what each organelle actually does will explain to you why cells are built the way they are.

Nucleus

1. Think of it as the cell's control center or headquarters.
2. It stores all the genetic instructions (DNA) for making proteins.
3. Without a nucleus, the cell can't make new proteins or divide to produce new cells.

Mitochondria

1. Think of them as the cell's power stations.
2. They break down glucose using oxygen to release energy in a form cells can actually use (ATP).
3. More mitochondria = more ATP = more energy available for cell activities.

Ribosomes

1. These are your protein-making factories.
2. They read instructions from DNA (via mRNA) and assemble amino acids into proteins.
3. More ribosomes = faster and more protein production.

Chloroplasts

1. Chloroplasts are like solar panels that capture light energy.
2. They convert light energy, carbon dioxide, and water into glucose (food) and oxygen.

Cell membrane

1. The cell membrane is like your body's bouncer or security guard.
2. It allows useful molecules (oxygen, nutrients) to enter while keeping harmful substances out.
3. It also controls what waste products leave the cell.

Cell wall

1. This is like the walls of a castle for plants, and is what gives plant cells their characteristic rectangular shape.
2. Prevents the cell from bursting when water enters by osmosis.

Vacuole

1. The vacuole functions like a water balloon.
2. It will push outward against the cell wall to keep the plant cell rigid and the plant upright.
3. The sap inside it (the water inside the balloon) then acts as a storage unit with nutrients, waste products, and pigments (like those in flower petals).

Cytoplasm

1. Lastly, the cytoplasm is like the factory floor of all the organelles within the cell.
2. It's mostly water with dissolved substances floating in it.
3. Chemical reactions happen here, and organelles are suspended in it.

How Do Organelles Control What a Cell Can Do?

The combination of organelles determines what the cell can do overall.

1. This is why more of an organelle = better at that function:
   1. Loads of mitochondria = good at releasing energy (e.g., muscle cells).
   2. Loads of ribosomes = good at making proteins (e.g., cells that produce hormones).
   3. Loads of chloroplasts = good at photosynthesis (e.g., leaf palisade cells).
2. No organelle = can't do that function:
   1. Animal cells have no chloroplasts, so they can't photosynthesize.
   2. Red blood cells have no nucleus, so they can't divide or make new proteins.

How Do Cells Become Specialized for Different Functions?

1. All cells in your body start as copies from the same fertilized egg, and eventually specialize through differentiation.
2. Once differentiated, most cells can't change back.
3. This starts during embryo development and continues in some tissues throughout life.
4. However, not all cells become differentiated, these undifferentiated cells are known as stem cells.

Structural changes during differentiation

1. Some cells gain organelles:
   1. Muscle cells develop lots of mitochondria.
   2. Palisade cells develop lots of chloroplasts.
   3. Protein-secreting cells develop lots of ribosomes.
2. Some cells lose organelles:
   1. Red blood cells lose their nucleus to make room for hemoglobin.
   2. Red blood cells also lose their mitochondria (they don't need to respire as much).
3. Cell shape changes:
   1. Nerve cells grow extremely long extensions (axons).
   2. Root hair cells develop long projections.
   3. Muscle cells become elongated and cylindrical.
4. Special structures develop:
   1. Sperm cells grow a tail (flagellum) for swimming.
   2. Ciliated epithelial cells grow tiny hair-like projections (cilia).

Example

• Muscle cells develop specialized features for contraction:
  • Multiple cells fuse together to create longer, stronger contractions.
  • Mitochondria increase to 1000-2000 per cell for constant ATP supply during repeated contractions.
  • Protein filaments (actin and myosin) develop to generate contracting force.
  • Cells become elongated so they can shorten significantly when contracting.

How Do Organelles Work Together?

Organelles don't work in isolation, they cooperate to carry out complex processes.

1. The nucleus, ribosomes, and mitochondria form a key partnership:
   1. Nucleus provides instructions from DNA.
   2. Ribosomes use those instructions to make proteins.
   3. Mitochondria provide energy (ATP) for these processes.