Something is firm if it is quite solid and doesn't move easily. Something is firmly attached if it doesn't wobble around or come loose. A sofa is firm if it is neither completely hard or soft. The sofa in the picture seems very firm.
Germ is the common name for a virus or bacteria, particularly one that can make you sick. A germ is also the start of life, such as a new shoot on a plant or a new idea. It is the root of the word germinate.
Glow-worm is a name given to any insect on the ground that glows, and you can see them at night. Some do look like worms, most are kinds of caterpillar or beetle. Firefly is also a word for the same insects, but glow worm is usually used for glowing insects on the ground, and firefly for glowing insects that fly.
Scientific name: bombyx mori
Silkworms are caterpillars that grow up into silkmoths. They live almost entirely on mulberry leaves. The cocoon they make can be used to make silk, a very attractive cloth that has been valued for thousands of years. A silkworm cocoon is made from a single strand of silk 1000 to 3000 feet long, and it takes 2000-3000 cocoons to make a pound of silk. The caterpillar in the cocoon is not allowed to emerge by itself, as this would damage the silk. The cocoons are boiled with the caterpillar inside.
Sperm is the reproductive cell of a male animal. Sperm fertilizes an ovum, otherwise known as an egg, to produce offspring, otherwise known as babies.