Which of the following statements are true with regard to mycobacterium?
1. they are classified as facultative anaerobes.
2. some are saprophytic.
3. they possess a gram-negative cell wall.
4. their cell wall contains a waxy lipid.
5. acid-fast staining is used in identification.

2, 4 and 5

Explanation:

The wall of Mycobacterium tuberculosis (a typical Mycobacterium) has a high lipid content, hence it does not respond to gram staining. Instead, acid-fast staining or Ziehl-Neelsen stain is used in its identification.

The cell wall of Mycobacterium species is thicker in comparison with other bacteria in the sense that it is hydrophobic, waxy and contains a unique acidic wax, known as mycolic acid.

Mycobacterium tuberculosis is an obligate aerobe, which means it is strictly dependent on oxygen. It thrives (multiplies) best under this condition.

Some species of Mycobacterium ate saprophytic i.e. they live on dead organic matter while some are obligate parasites that live on tissues e.g M.tubercosis and M.leprae causes tuberculosis and leprosy in humans respectively.

the element that provides strength to the exoskeletons of clams and oysters is phosphorus.

this is so because calcium carbonate is the main component in the shells. calcium carbonate is strengthened by phosphorus.

explanation:

both male and female gametes are produced by meiosis of the germ cells. therefore, both male and female gametes are haploid. one male and one female gamete unite during the fertilization to form the diploid zygote. in seed bearing plants, pollen grain is the male gametophyte, which produces sperm cells.