Homeostasis is the internal maintenance of a stable equilibrium despite external changes. For humans to maintain homeostasis, the body must detect changes and counteract them, which usually involves a negative feedback loop. For example, if your body temperature gets too low, a negative feedback loop will help your body raise its temperature. Heat is conserved by constricting blood vessels and shivering, which helps to warm the body.
The hypothalamus plays a large part in maintaining homeostasis in the body. It links the endocrine and nervous systems. Its role is to keep the body in balance and to do this it helps stimulate or inhibit many processes, such as heart rate and blood pressure, body temperature, and appetite and body weight. When the hypothalamus receives a signal from the nervous system, a neurohormone is secreted that will start or stop the secretion of a pituitary hormone.
One example of how the body maintains homeostasis is when blood sugar levels become too high. The body converts carbohydrates from the food we eat into glucose. When blood sugar levels are high, the pancreas secretes insulin into the body. The insulin binds to the glucose in the blood to allow it to be absorbed and stored as glycogen, lowering the blood sugar. Conversely, when blood sugar levels are too low, the pancreas secretes glucagon. Glucagon breaks down glycogen into glucose in the liver and frees them into the bloodstream. This raises blood sugar levels.
Important Groups of Bacterial Life
There are many different types of bacteria. Some might seem very unusual in how they have adapted to their environment. Chemosynthetic bacteria have evolved to obtain their energy from inorganic molecules such as ammonia and sulfur. These types of bacteria usually live in remote environments where there is no sunlight, as in the case of bacteria that live in deep-sea vents. Hydrogen sulfide comes out of these vents and the chemosynthetic bacteria are able to oxidize it to sulfur. During this oxidation, they use the chemical energy released to make sugar molecules from carbon, hydrogen, and oxygen.
Cyanobacteria are bacteria that live in water and photosynthesize. Some are able to live freely while others live in a symbiotic relationship with fungi or plants. This type of bacteria is one of the largest groups of bacteria on earth, thought to be responsible for generating half the world’s oxygen. Cyanobacteria are also the source of chloroplast for plants. At some point during the late Proterozoic or early Cambrian era, cyanobacteria lived inside of certain eukaryotic cells. Eventually, these eukaryotic cells evolved into red algae, green algae, and plants.
Some bacteria, like Clostridium and Bacillus, are able to form spores called endospores. These spores contain all the genetic material found in the vegetative state of the bacteria, but the spores are dormant. The endospores can stay dormant for years waiting for the right conditions to grow. Scientists have found endospores centuries or thousands of years old. They are extremely resistant to UV radiation, desiccation, high temperatures, and chemicals.
As humans use antibiotics more often, some bacteria are becoming resistant to antibiotics. Staphylococcus aureus is an example of antibiotic-resistant bacteria. It can cause flesh-eating disease and pneumonia. Antibiotic resistance can occur in several ways: antibiotic concentration, bacterial mutation, or bacterial genetic exchange. Antibiotic concentration occurs when there is a biofilm that the bacteria live in. The biofilm is a thick jelly-like substance that an antibiotic cannot penetrate all the way through. The bacteria in the outer parts of the biofilm can be reached by the antibiotic, but the bacteria in the center are exposed to only a portion of antibiotic.
Bacteria cells replicate very fast and bacteria can evolve much quicker than animals can. Bacterial mutation, such as a change in the cell wall, can sometimes make antibiotics less effective. Bacteria can also share genetic material with each other, even between different species. This is called bacterial genetic exchange. If one species of bacteria has become resistant to antibiotics, it can pass those genes to another type of bacteria.
Vascular plants are made of four types of tissues: dermal, ground, and vascular.
- Dermal tissue is made of cells that cover the outside of the plant. This layer of cells is called the epidermis. A waxy substance called cuticle is secreted from the epidermis cells. Cuticle is a protective layer that prevents water loss in the plant and keeps infections and toxins out.
- Stomata are tiny pores on the underside of leaves that open and close to allow the plant to take in carbon dioxide and release oxygen.
- Root hairs are a type of specialized dermal cell that are long and microscopic. They absorb water and nutrients from the soil.
- Ground tissue is important in metabolism. It provides structural support and can store food and water.
- Mesophyll is ground tissue located in leaves. Chloroplasts are found in each mesophyll cell. This is where photosynthesis occurs.
- Meristem is found in buds and the tips of roots. The role of the meristem is to start the growth at the tips of roots and shoots and to form buds.
- Vascular tissue is made up of xylem and phloem.
- Xylem carries water and minerals throughout the plant.
- Phloem carries food throughout the plant.
A tropism occurs when a plant grows toward or away from an external stimulus. Three types of tropisms are geotropism, phototropism, and thigmotropism.
Geotropism is how plants grow in relation to gravity. Roots growing down is an example of positive geotropism, while shoots growing up are an example of negative geotropism.
Phototropism is the growth of a plant toward or away from light. Positive phototropism is when a plant grows toward light, while negative phototropism is when a plant grows away from light.
Thigmotropism describes a plant moving in reaction to being touched. This is shown in sweet pea tendrils. The tendrils have a tendency to climb, so when they touch something solid they grow toward it.