BIOLOGY [5 Mark Question Answer]

Bacteria are harmful to the human beings in the following :
(i) Certain bacteria can cause diseases in human beings. Tuberculosis, tetanus, whooping cough, cholera, plaque,
leprosy, diphtheria and pneumonia are bacterial diseases. Bacteria also causes diseases to plants.
(ii) Spoilage of food, rotting of fruits, vegetables meat is also caused by bacteria. Improperly canned food items sometimes have certain anaerobic bacteria which release certain toxic substances causing a dangerous disease called botulism. Poultry products also carry disease-causing germs which may cause stomach infection, a kind of food poisoning.
(iii) Gastroenteritis, urinary tract infections are also caused by bacteria- Escherichia coli. Typhoid and food poisoning are caused by salmonella. Tuberculosis, a lung disease is caused by Mycobacterium tuberculosis.

The three groups of algae are :
(i) Red algae
(ii) Green algae
(iii) Brown algae

Red algae	Green algae	Brown algae
1. Contain chloro- phyll as well as red and blue pigments.	Contain only chlorophyll	Contain brown pigments along with chlorophyll.
2. For example: laminaria, fucus.	For example: chondrus	For example: chlamydomonas
3. Found in sea as well as fresh water	Found mostly in fresh water	Found in sea water

Bacteria lack chlorophyll and hence cannot prepare their own food. They depend on other sources for their food. They may be saprophytes i.e. derive their food from dead and decaying matter or they may be parasites i.e. obtain their food by living on or inside the body of other organisms. Thus most of the bacteria are heterotrophs. However, there are some bacteria which are autotrophic and are able to synthesise their own food.
Bacteria can survive under harsh conditions due to the formation of a hard protective covering around them called a cyst or a spore. They remain inactive in the cyst during unfavourable conditions. The hard protective covering protect it from the unfavourable conditions and it becomes active during favourable conditions by breaking the cyst wall.