The corrrect option is D.
Since the scientist was trying to determine if substance A affect the rate of reaction of X and Y, the best thing to do is to make substance X and Y to react together first, he should then measure the time taken for the reaction to take place. Next, he should make X and Y to react together again, but this time in the presence of A. The time taken for the reaction to occur should be measures. The scientist can now compared the two time measurements and decide if there are difference between them or not.
Answer:
A
Explanation:
The end of the germinal period is marked by the implantation of the blastocyst in the wall of the uterus.
Answer:
Cnidaria
→ Organisms have specialized stinging cells
→ Two type of body plans exist - polyp and medusa
Porifera
→ Organisms lack symmetry
→ Adult forms are sessile
→ Organisms obtain food by filtering water
→ Phenomenon of alternation of generation is observed.
Explanation:
Cnidaria, also known as the coelenterata, is a phylum of mostly marine animals having about 9,000 living species. Some of them include the corals, hydras, jellyfish, sea anemones, sea whips, etc. They possess specialized cells known as cnidocytes ( also known as “stinging cells”). These cells can seen around the mouth and tentacles cnidarian. They immobilize their prey with toxins. These Cnidaria have two body plans and which are polyp and medusa.
The phylum Porifera are known as the pore bearers. It has about 5000 species. Their adult forms are sessile. They live permanently attached to rocks. They can under alternation of generation. They possess no organs in their bodies. Also, they lack symmetry. They can be referred t as filter feeders because they obtain food by filtering water.