Budding, spores and clones

Budding. In yeast, a small round bump (a bud) grows out of the parent cell. In *Hydra*, cells divide again and again at one spot, making a bud that grows, then breaks away to live on its own. Several buds can grow at once.

"Where does mould on bread come from?" People once believed living things could appear from non-living matter. Louis Pasteur proved that new life always comes from existing life. He also gave the germ theory of disease, which is why we sterilise food and medical instruments.

Spore formation. Leave a slice of damp bread for a few days and fuzzy mould grows. It grew from spores floating in the air. Under a microscope you see thread-like hyphae with tiny sacs on top full of round spores (*Rhizopus), or spores on a swollen tip (Aspergillus*).

Spores are made in millions. They are light, usually single cells, and float in the air until they land somewhere damp with food.

Mould grows best when it is warm (25 to 35 °C) and moist. Cold slows it down or stops it. That is why we keep food in the fridge.

Fungi are not just pests. They break down waste and pollution, remove heavy metals from factory waste, and give us antibiotics such as penicillin and amoxicillin.

All asexual reproduction depends on mitosis, which makes cells with exactly the same chromosomes as the parent. So the young are clones (exact copies). This is fast, and lets numbers grow quickly when conditions are good.

But there's a risk: if all the hydras are identical, one disease that kills one can kill them all.