The body "shivers". Shivering is the rapid contraction and vibration of muscles in order to create warmth within the body. Obviously this would only be effective up to tempratures which your skin would be-able to handle.
Bird's feathers act as insulators against the cold. They often survive cold weather by finding a protected area out of the cold weather.
Not by itself. But being cold will will put a strain on your body, leaving less energy for the immune system to protect you from diseases.
Being cold will burn mroe calories as the body needs to warm itself up, but if it is too cold then the body will begin to conserve calories in order to stay alive. It is easier for the body to burn calories in warmer weather.
No. Neither does feeling cold in cold weather, or going outside for a brief time without a jacket in colder weather. Colds are caused by viruses. For lowered body temperatures to affect the immune system as some people believe, you would have to be experiencing hypothermia which is caused by long term exposure to extreme weather or cold water that reduces your core body temperature to below 95 F.
Water.
Water
In cold weather, the arteries and veins nearer the skin have less blood passing through them and the ones further into the body have more thereby retaining heat. The hairs on most parts of your body also stand up to trap a layer of air for insulation. The body when cold frequenly shivers. This is a bodies way of trying to produce movement which in turn generates blood flow and heat transfer. In warm weather, the opposite happens. Hairs lie down and the arteries and veins nearer the skin fill up thereby letting heat energy conduct radiate out of the body. The body has pours. These secret sweat which acts as a cooling agaent.
Thick fur
Cats tend to groom themselves more in warm weather to help regulate their body temperature and stay cool. However, grooming is also essential for maintaining their hygiene regardless of the season.
Celsius is a scale of measuring temperature, not a temperature in and of itself.
In cold weather, your body sends extra blood to the extremities (the farthest protruding areas) in your body. The tip of your nose is one of them. So when its cold out, your body sends more blood to your nose, which makes it appear red or pink.
During cold weather. During warm weather, the body perspirates (sweats) to maintain body temperature and hence a lot of fluids are lost. so, the amount of fluids the body has to expel via urine is lesser. However, during cold weather, there is no perspiration and hence the amount of fluids the body expels via urine is higher than during warm weather.