IB Biology Topic D2.1.14: Cell Growth During Interphase Notes

Interphase Is a Busy Growth Phase, Not a Rest Stop

1. During interphase the cell is metabolically active and grows steadily.
2. It is a common mistake to call it a resting phase, because the cell is constantly carrying out biosynthesis.
3. Interphase covers the G1, S and G2 phases, which is where all this growth takes place.
4. By the time the cell divides, it has grown large enough for each daughter cell to be a viable size.

Growth Happens Through Biosynthesis

1. The cell roughly doubles its size and mass across interphase.
2. This growth depends on biosynthesis, the building of new cell components.
3. There are three main things the cell makes more of: proteins, DNA, and organelles.

Three Building Jobs: Proteins, DNA and Organelles

1. Protein Synthesis
   1. Ribosomes build the proteins the cell needs to grow.
   2. Enzymes such as DNA polymerase are made ready for DNA replication.
   3. Structural proteins accumulate to support the larger cell.
2. DNA Replication
   1. In S phase, the cell copies all of its DNA.
   2. This makes a full set of genetic instructions for each future daughter cell.
3. More Organelles
   1. The cell increases its number of organelles and its volume of cytoplasm.
   2. Mitochondria grow and divide to make more copies.
   3. In plant cells, chloroplasts also grow and divide.
   4. These organelles form only from existing organelles, never from scratch.

Why the Growth Matters for Division

1. Growth during interphase gives each daughter cell enough organelles to function.
2. It also ensures each daughter cell reaches a viable size after division.
3. Without this growth, division would produce cells too small to survive.