Hardest Part of the Human Body?
Answer: A
Tooth enamel is the hardest substance in the body.
It is about 96 per cent mineral, mostly hydroxyapatite crystals packed into rods, and rates 5 on the Mohs scale. Being acellular it cannot repair itself, which is why a cavity never heals.
Please log in or register to report this question.
Select the correct statement about the Heart Valves.
Answer: B
The correct statement is that the atrioventricular valves are supported by the chordae tendineae, which stop them turning inside out when the ventricles contract.
The tricuspid valve lies between the right atrium and right ventricle and the mitral between the left atrium and left ventricle - the reverse of what two of the other options say.
Please log in or register to report this question.
What provides electrons for the light reactions?
Answer: A
Water supplies the electrons for the light reactions.
Chlorophyll loses an electron when it absorbs a photon, and replaces it by splitting water:
\[ \mathrm{2H_2O \rightarrow 4H^+ + 4e^- + O_2} \]
The oxygen released is the by-product, and every molecule of it in the atmosphere came from this reaction.
Please log in or register to report this question.
Which of the following hormones is called the emergency hormone?
Answer: B
Adrenaline is called the emergency hormone.
Released from the adrenal medulla under stress, it speeds the heart, raises blood pressure and blood sugar, widens the airways and diverts blood to the muscles - the fight-or-flight response that prepares the body for sudden effort.
Please log in or register to report this question.
In which of the following organelles does photosynthesis take place?
Answer: B
Photosynthesis takes place in the chloroplast.
Its thylakoid membranes hold the chlorophyll that captures light, and the stroma around them holds the enzymes of the Calvin cycle that fix carbon dioxide into sugar. A leaf cell may contain fifty or more.
Please log in or register to report this question.
DNA can be found in what Organelles?
Answer: A
Outside the nucleus, DNA is found in the chloroplasts and mitochondria.
Both carry a small circular chromosome of their own, along with their own ribosomes. This is the chief evidence for the endosymbiotic theory, which holds that they were once free-living bacteria taken up by an ancestral cell.
Please log in or register to report this question.
Which of the following is an Autotroph?
Answer: B
Algae are autotrophs - they contain chlorophyll and make their own food by photosynthesis.
Fish and butterflies are consumers, and a mushroom is a saprophytic fungus with no chlorophyll at all.
Please log in or register to report this question.
Where are Enzymes found?
Answer: B
Enzymes are found in the living body, in every cell.
They are proteins that catalyse the reactions of metabolism - digestion, respiration, synthesis and repair - each acting on one substrate and speeding its reaction by many millions of times without being used up.
Please log in or register to report this question.
Study of inter relationship between living organism and their environment is called _______
Answer: C
The study of the relationship between organisms and their environment is ecology.
Haeckel coined the word in 1866 from the Greek oikos, household. An ecosystem is one unit of study within ecology, not the study itself.
Please log in or register to report this question.
Transmission of stimuli from one part of body to other part takes place through __________
Answer: D
Stimuli are transmitted from one part of the body to another by nervous tissue.
Its neurons carry impulses as waves of electrical change along the axon and pass them to the next cell across a synapse. The impulse travels at up to 120 metres a second in a myelinated fibre.
Please log in or register to report this question.
