Answer:
a) Myelinated nerve fibres
b) The white matter
c) gray matter
Explanation:
The three main parts of cerebral hemispheres are
a) Myelinated nerve fibers
b) The white matter
c) Gray matter
The nerve fibers of the white matter are responsible for connecting the functional parts of cerebral cortex while the gray matter is further divided into four surface folds/lobes with each lobe associated with a specific activity. Such as frontal lobe take cares of motor activity and speech, parietal lobe is responsible for touch and position sensation, occipital lobe for vision and temporal lobe for hearing.
Answer:
sieve-tube elements, companion cells
Explanation:
Sieve-tube elements and companion cells are responsible for the movement of photosynthes through a plant.
The sieve tube elements are shorter (almost organelle-free) living cells, placed end to end, forming the sieve tubes. Their transverse cell walls are called sieve plaques that make connections between cells and through openings called sieves establish the connection between the cytoplasm of adjacent cells. Each sieve is coated with calose (glucose polymer), which in winter can completely clog the vessel and then dissolve in spring. When infections occur or the vessel is parasitized, it can also be clogged with callose.
Companion cells are specialized parenchymal cells, which contain all the components that exist in living cells, including the nucleus, are the cells most closely linked to the sieved tube element. The Screened Tube Element and its companion cells are related in development, are derived from the same mother cell, and have several cytoplasmic connections to each other. Due to the many connections, the potential function of the companion cells is to release substances into the sieved tube element and, when the nucleus is absent, to include information molecules, proteins and ATP. When a screened element dies, its companion cells also die, which is a demonstration of this interdependence.
This process is called meiosis. Mitosis produces two identical daugheter cells, each with 12 chrimosomes. Meiosis produces four daughter cells with 6 chromosomes.
Answer:
Leeuwenhoek made his own microscope lenses, and he was so good at it that his microscope was more powerful than other microscopes of his day. In fact, Leeuwenhoek's microscope was almost as strong as modern light microscopes.
Explanation:
Hope this helps you
A Nerve electrical impulse only travels in one direction. There are several reasons nerve impulses only travel in one direction. The most important is synaptic transport.
In order for a "nerve impulse" to pass from cell to cell, it must cross synaptic junctions. The nerve cells are lined up head to tail all the way down a nerve track, and are not connected, but have tiny gaps between them and the next cell. These tiny gaps are called synapses.
When you get a nerve firing, you have probably heard that it is an electrical impulse that carries the signal. This is true, but it is not electrical in the same way your wall outlet works. This is electrochemical energy. Neurotransmitters are molecules that fit like a lock and key into a specific receptor. The receptor is located on the next cell in the line. When the neurotransmitter hits the receptor on the next cell in line, it signals that cell to begin a firing as well.
This will continue all the way down the length of the nerve track. In a nutshell, a nerve firing results in a chain reaction down the nerve cell's axon, or stemlike section. Sodium (Na+) ions flow in, potassium (K+) ions flow out, and we get an electrochemical gradient flowing down the length of the cell. You can think of it as a line of gunpowder that someone lit, with the flame traveling down the length of it. Common electrical power is more like a hose full of water, and when you put pressure on one end, the water shoots out the other.
Therefore, nerve impulses cannot travel in the opposite direction, because nerve cells only have neurotransmitter storage vesicles going one way, and receptors in one place.
