Answer:
B. The membrane lets certain substances move across it freely, while others must move through a “gate”.
Explanation:
Selective permeability is a property of cellular membranes that only allows certain molecules to enter or exit the cell. This is important for the cell to maintain its internal order irrespective of the changes to the environment. For example, water, ions, glucose and carbon dioxide may need to be imported or exported from the cell depending on its metabolic activity. Similarly, signaling molecules may need to enter the cell and proteins may need to be released into the extracellular matrix. The presence of a selectively permeable membrane allows the cell to exercise control over the quantum, timing and rate of movement of these molecules.
“The nth term of the following types of sequences can be found out using the following Formulas:
1.Arithmetic Progression(AP) : here, the consecutive terms differ by a common difference (d).
tn= a+(n-1)d
Where,
a= is the first term of the sequence,
n= nth term
d= common difference
2. Geometric Progression(GP):
Here, the consequtive terms differ by a common ratio (r).
Tn= ar^(n-1)
where,
a = first term
r = common ratio
tn= nth term
3.Harmonic Progression (H.P):
It is the reciprocal of AP.
To find nth term of a HP, first convert it into AP and then apply the tn formula for the sequence and take the reciprocal of the obtained tn again.
Hope the answer helps you!!”
The correct terms to fill in the blanks are gastric cavity and extracellular. In cnidarians, the mouth of both the medusa and polyp form opens into an internal gastric cavity where extracellular digestion takes place. The polyp and medusa are body forms that can be found in the phylum Cnidaria. The polyp is a nonmotile body form while the medusa is a free swimming body form.
