Answer: False
Explanation:
Protozoans are not the organism that fix nitrogen for the plants. The organism that fix nitrogen to convert it into a form which can be used by plants are known as diazotrophs.
These are bacteria and archae that fix nitrogen gas found in the atmosphere into more usable form such as ammonia.
These organism can grow without any external source of fixed nitrogen. Example: Rhizobia and azospirillium.
A scientific theory is an explanation of an aspect of the natural world that can be repeatedly tested and verified in accordance with the scientific method, using accepted protocols of observation, measurement, and evaluation of results. Where possible, theories are tested under controlled conditions in an experiment.
Descending tracts are the pathways by which motor
signals are pass through from the brain to lower motor neurones. Thus, all
the neurones within the descending motor system are classed as upper motor
neurones. The lower motor neurones then directly innervate muscles to produce
movement. Their cell bodies are found in the cerebral cortex or the brain stem,
with their axons remaining within the CNS.
Answer: when bright light is present, the pupil reduces in size, or flinching when feeling threatened
Explanation: i know what reflexes are :)
Ans.
Steroids are defined as active organic bio-molecules, having four rings with a specific molecular configuration. Steroids play role in two major functions: as hormones or signaling molecules and as structural components of plasma membrane.
Examples of steroid hormones are estrogen, progesterone, and cortisol. Thus, the correct answer is 'option b). they serve as chemical messengers.'
