Roundworms: the human roundworm (Ascaris)
Roundworms have a body round in cross-section and thread-like, with the internal organs in a body cavity. They live in the sea, freshwater and soil, and some are parasites of humans, animals and plants. The human roundworm lives in the small intestine: the female is 20–40 cm, the male 15–25 cm, and the male’s tail is curved. The body is covered with a tough cuticle, so digestive juice does not damage it. The digestive system is a long tube from the mouth to the anus – unlike flatworms it is open at both ends. Ascaris has separate sexes and lays up to 240,000 eggs a day. Eggs leave with faeces into the soil; if they reach a person’s intestine through dirty hands or unwashed vegetables, larvae hatch, travel by the blood to the lungs, are coughed up into the mouth and swallowed, and mature in the intestine. The illness brings stomach pain and weight loss; treatment is decided by a doctor. To avoid it wash hands with soap and wash vegetables and fruit well.
Draw the roundworm life cycle: egg → soil → dirty hand/vegetable → intestine → blood → lung → mouth → intestine. At each arrow write a hygiene rule (hand washing, washing vegetables). Safety: wash hands with soap after working with soil; never put soil in the mouth.