Explanation:
In the megasporan- gium of each ovule, the megasporocyte divides by meiosis, producing four megaspores. One survives and forms a female gametophyte. Fertilization: In nucleus of developing endosperm-- Double fertilization occurs. One sperm fertilizes the egg, forming a zygote.
Answer:
The correct answer is D. proliferation and differentiation.
Explanation:
Primary immune response occurs due to the first exposure of an antigen to the immune system. The primary immune response is generally delayed by many days because it takes time for B and T cells to become cloned and to proliferate and differentiate.
Then after several days of proliferation and differentiation of activated T and B cells, T cells become effector T cells and B cell becomes plasma cells which then eliminates the antigen. Memory B and T cells are also produced during this process which helps in generating a quick immune response during the second and subsequent exposure of that antigen.
So the correct answer is D. proliferation and differentiation.
Most people will have a minor neck problem at one time or another. Our body movements usually do not cause problems, but it's not surprising that symptoms develop from everyday wear and tear, overuse, or injury. Neck problems and injuries most commonly occur during sports or recreational activities, work-related tasks, or projects around the home.
Neck pain may feel like a "kink," stiffness, or severe pain. Pain may spread to the shoulders, upper back, or arms, or it may cause a headache. Neck movement may be limited, usually more to one side than the other. Neck pain refers to pain anywhere from the area at the base of the skull into the shoulders. The neck includes:
The bones and joints of the cervical spine (vertebrae of the neck).
The discs that separate the cervical vertebrae and absorb shock as you move.
The muscles and ligaments in the neck that hold the cervical spine together.
Neck pain may be caused by an injury to one or more of these areas, or it may have another cause. Home treatment will often help relieve neck pain caused by minor injuries.
Activities that may cause neck pain
Neck pain is often caused by a strain or spasm of the neck muscles or inflammation of the neck joints. Examples of common activities that may cause this type of minor injury include:
Holding your head in a forward posture or odd position while working, watching TV, or reading.
Sleeping on a pillow that is too high or too flat or that doesn't support your head, or sleeping on your stomach with your neck twisted or bent.
Spending long periods of time resting your forehead on your upright fist or arm ("thinker's pose").
Stress. Tension may make the muscles that run from the back of the head across the back of the shoulder (trapezius muscle) feel tight and painful.
Work or exercise that uses your upper body and arms.
Sudden (acute) injuries
Minor neck injuries may result from tripping, falling a short distance, or excessive twisting of the spine. Severe neck injuries may result from whiplash in a car accident, falls from significant heights, direct blows to the back or the top of the head, sports-related injuries, a penetrating injury such as a stab wound, or external pressure applied to the neck, such as strangulation.
Pain from an injury may be sudden and severe. Bruising and swelling may develop soon after the injury. Acute injuries include:
An injury to the ligaments or muscles in the neck, such as a sprain or strain. When neck pain is caused by muscle strain, you may have aches and stiffness that spread to your upper arm, shoulder, or upper back. Shooting pain that spreads down the arm into the hand and fingers can be a symptom of a pinched nerve (nerve root compression). Shooting pain is more serious if it occurs in both arms or both hands rather than just one arm or one hand.
A fracture or dislocation of the spine. This can cause a spinal cord injury that may lead to permanent paralysis. It is important to use correct first aid to immobilize and transport the injured person correctly to reduce the risk of permanent paralysis.
A torn or ruptured disc. If the tear is large enough, the jellylike material inside the disc may leak out (herniate) and press against a nerve or the spinal cord (central disc herniation). You may have a headache, feel dizzy or sick to your stomach, or have pain in your shoulder or down your arm.
