Answer:
The correct answer is option B, that is, promoter, operator, gene.
Explanation:
In a prokaryote, just in front of the operator, the promoter is located, and just in front of the structural genes, the operator is located. All these in combination give rise to an operon.
Any gene, which codes for an enzyme or a structural protein is termed as a structural gene, in the lac operon, a structural gene codes for three distinct kinds of enzymes. A short sequence of DNA is situated just in front of the structural gene, which is known as the operator. An operator functions as a switch for transcription, that is, it monitors whether the process of transcription will take place or not.
Just in front of an operator, a sequence of a promoter is present, and for the transcription and translation of all the structural genes, the RNA polymerase needs to combine first with the promoter. In case, if no transcription is to take place, then the operator allows the repressor to bind with it and prevent the attachment of RNA polymerase with the promoter. Hence, the correct sequence of a prokaryotic operon is a promoter, operator, and gene.
First Part of the Cell Theory:
All living things are composed of cells.
Second Part of the Cell Theory:
Cells are the basic unit of structure and function in living things.
Third Part of the Cell Theory:
All cells are produced from other cells.
The process that is similar to binary fission is Mitosis
The correct answer is option (d) They allow the exchange of gases between cells in the leaf and the external environment.
Stomata are the tiny openings present in the epidermis (outer layer of cells) of the leaf. They have a pore which is guarded by the guard cells which controls the opening and closing of the stomata. Air enters and exits through the stomata.
The main funtion of stomata is to facilitate the gaseous exchange. The gas exchange that occurs when the stomata are open helps in the process of photosynthesis. During photosynthesis, carbon dioxide is taken in from the atmosphere and oxygen is released as a by-product of photosynthesis. The glucose produced is converted into the starch and stored in the leaves.
Also, water vapour diffuses through the stomata into the atmosphere by a process called the transpiration.
Thus, stomata are the structures that are mainly involved in the gaseous exchange between the cells of the leaf and the atmosphere.
