Exam for genbio2

• Reproduction is the biological mechanism by which the parents create new species known as the offspring. It consists of two forms: sexual and asexual reproduction. The distinction between the two forms lies in the required number of parents for both types.

   Two parents are required for sexual reproduction to give birth to the offspring. One single parent will give birth to the offspring in asexual reproduction. Asexual reproduction is commonly seen in plants, but in the animal kingdom, it is less common.
• Binary Fission - Bacteria and amoeba typically use this method of reproduction. The DNA of the parent bacteria replicates itself in this form of reproduction and then the cell divides into two halves, each half having its own DNA. Therefore, the parent cell divides into two identical daughter cells. These daughter cells are identical to the parent cell.
• Budding - In this type of asexual reproduction process, the offspring grows on the parent body from a bud-like structure. This is usually seen in Echinodermata and hydra. The buds fall off the parent body once large enough, and begin their independent life
• Parthenogenesis - The female organism of the species generates eggs without fertilization in this process of asexual reproduction, and the offspring emerge from that. Lizards, few insects and some fishes reproduce in this way. This reproductive form is not seen in mammals. This kind of asexual reproduction is seen in both plants and animals.
• Fragmentation - The parent organism splits into several fragments or segments in this form of asexual mode of reproduction, where each of the fragments evolves into a new organism. Starfishes, which exhibit sexual reproduction, also exhibit this type of asexual reproduction in which 6 an entirely new organism may be produced by a part of its body, such as its arm
• Vegetative Propegation - This process of asexual reproduction takes place in the stems of

  certain plants from certain buds that emerge on their leaves or stems,

  giving rise to new plants. Tuber (potato), bulb (onion), stolon or runner

  (strawberry), rhizome(ginger), sucker (banana), stem cutting (rose) and

  leaf (welcome plant) are used as an example of such propagation.
• Sexual reproduction involves two separate parents that belong to the opposite sex. Both plants and animals exhibit this kind of reproduction. Flowering plants undergo sexual reproduction

  
  

  A flower is the sexual reproductive organ in plants. Flowers are often the most attractive structures of a plant. The flower’s anatomy can be divided into following parts: Calyx, Corolla, Gynoecium, Androecium.
• Calyx

  These are green petal-like structures located right above the receptacle called the base of the flower. Calyx is made up of 7 sepals. Their primary task is to safeguard the flower while it is still in the bud process.
•  

  Corolla is the name given to the collective colorful petals of the flower. The petals of various flowers are found in different colors and are often fragrant much of the time. It is the petals that attract the pollinating agents. The corolla is found above the calyx layer.
• Androecium - The male reproductive section of a flower is the androecium. It is made up of a series of stamens. Each stamen at the top of it consists of a filament and anther. The anthers are lobed structures that produce the male gamete-containing pollen.
• The gynoecium is the female reproductive organ of the flower. It is composed of the ovary, style, and stigma. The style is a slender filament on top of which lies the stigma that works to retain pollen grains that are transferred. Once the pollen lands on the stigma, it is moved downward to the ovary via the style. The ovary is lobed and composed of the female gamete-containing ovules.
• The penis is the male organ for sexual intercourse and urination.

  Semen and urine leave the penis through the urethra.

  The scrotum is a loose,

  pouch-like sack of skin that covers the testicles and hangs behind the penis.
• The testis must

  maintain a temperature slightly cooler than natural body temperature in order to produce sperm.

  Special muscles contract and relax in the wall of the scrotum to move the testicles close to the body.

   Located at the back of the testis is the epididymis that binds to the vas deferens. Its function is to store sperm and carry it.

  The testis is the site of testosterone production. Seminiferous tubules are the coiled collection of tubes within the testicles. Spermatogenesis takes place within these tubules.
• The male reproductive system's internal organs are called accessory organs.

   They include the vas deferens, prostate gland, seminal vesicles, and bulbourethral (Cowper's) glands.
• The vas deferens transports mature sperm to the urethra during ejaculation.

  Seminal vesicles are sac-like pouches that bind near the base of the bladder to the vas deferens. The vesicles produce molecules which serve as energy sources for sperm, such as fructose. Much of the amount of a man's ejaculate consists of the seminal vesicle fluid.

  The prostate gland is a walnut sized organ in front of the rectum situated below the urinary bladder.
• It adds extra fluid to the ejaculate, which acts as sperm nourishment. Bulbourethral (Cowper's) glands are pea-sized structures situated just below the prostate gland on the sides of the urethra. These glands contain a slick, clear fluid that  empties into the urethra directly. The fluid produced by these glands lubricates the urethra and neutralizes residual urine-related acidity
• There are two main parts of the human female reproductive system: the uterus and the ovaries, which contain egg cells for a woman.

  The uterus hosts the fetus that is developing. It also produces vaginal and uterine secretions. It also passes the anatomically male sperm through to the fallopian tubes.
• The ovaries produce the anatomically female eggs. They also produce and secrete progesterone and estrogen. These sections are internal; the vagina, which contains the labia, clitoris, and urethra, enters the external organs at the vulva. The vagina is connected via the cervix to the uterus, while the uterus, through the fallopian tubes, is attached to the ovaries. The ovaries produce an ovum at certain times, which passes into the uterus through the fallopian tube.
• If it meets sperm during this transit, the sperm penetrates and merges with the egg, fertilizing it. Generally, fertilization occurs in the oviducts, but can occur in the uterus itself. Then the zygote implants itself in the uterine wall, where the embryogenesis and morphogenesis process starts. When sufficiently developed to survive outside the womb, the cervix dilates and uterine contractions drive the fetus through the birth canal (vagina).
• In mammals, a layer of extracellular matrix composed primarily of glycoproteins called zona pellucida protects the egg. A series of biochemical processes, called acrosomal reactions, take place when a sperm binds to the zona pellucida. The acrosome produces digestive enzymes in placental mammals that initiate the degradation of the glycoprotein matrix that protects the egg and enables the sperm plasma membrane to fuse with the egg plasma membrane.
• Cells in the blastula are spatially rearranged to create three layers of cells. This is called gastrulation. The blastula folds upon itself during gastrulation to form the three cell layers

  The ectoderm gives rise to the epidermis and the nervous system. The mesoderm produces the body's muscle cells and connective tissue. The endoderm gives rise to columnar cells and several internal organs including the digestive system
• Through the process of differentiation, organs form from the germ layers. Embryonic stem cells express unique sets of genes during differentiation, which will decide their ultimate type of cell. For example, genes unique to skin cells will be expressed by certain cells in the ectoderm. As a result, epidermal cells would be divided into these cells.
• Autotrophic Nutrition - species use simple inorganic materials such as water and carbon dioxide to synthesize food on their own in the presence of light and chlorophyll. In other words, to transform light energy into food, such as glucose, the photosynthesis mechanism is used. The organisms are called autotrophs. Some examples of autotrophic feeding are plants, algae, and bacteria (cyanobacteria)
• Each organism is unable to prepare food on its own. For their nutrition, such species rely on others. Heterotrophs are species which cannot produce food on their own and rely on other sources/organisms. Heterotrophs include fungi and all animals, including humans. Depending on their climate and adaptations, heterotrophs can be of several types. Some may eat plants (herbivores) and others may eat animals (carnivores), although few eat both (omnivores).
• Normal breathing rates

  12-25 times per minute
• Diffusion

  The movement of molecules in the direction following the concentration gradient, from a region of greater concentration to a region of lower concentration
• Diffusion through a moist membrane

  The fundamental process of gas exchange
• Gas exchange in plants

  1. Gases do not pass through the leaf cuticle; they pass through pores called stomata in the epidermis

  2. Stomata are numerous on the lower surface of the leaf and usually open during the day when the rate of photosynthesis is highest

  3. The opening and closure of stomata are due to physiological changes in the surrounding guard cells
• Gas exchange in animals

  • Oxygen and carbon dioxide diffuses across moist membranes
  • The exchange happens directly with the environment in simple animals
  • The exchange between the environment and the blood happens with complex organisms, such as mammals
  • The blood transports oxygen to deeply embedded cells and transports carbon dioxide out of the body
• Osmoregulation

  Control of the osmotic pressure of body fluids of an organism to preserve the homeostasis of the body's water content
• Gas exchange in earthworms

  • Oxygen diffuses into tiny blood vessels on the surface of the skin where it mixes with hemoglobin
  • Hemoglobin loosely binds to oxygen and brings it across the bloodstream of the animal
  • Hemoglobin transports carbon dioxide back to the blood
• Types of osmoregulation

  • Osmoconformers
  • Osmoregulators
• Gas exchange in arthropods

  • Terrestrial arthropods have a set of openings on the surface of the body called spiracles
  • Spiracles open into tiny air tubes called tracheae, which grow into fine branches that reach into all areas of the body of the arthropod
• Osmoconformers

  • Species that attempt to balance the osmolarity of their bodies with their surroundings
  • Adhere by active or passive means
  • Most aquatic invertebrates are osmoconformers
• Gas exchange in fish

  • Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills
  • Within the gill filaments, capillary blood flows in the opposite direction to the water, causing counter-current exchange
• Osmoregulators

  • Species that actively control their osmotic pressure, regardless of the external environment
  • Many vertebrates, including humans, are osmoregulatory
  • Many freshwater fish are also osmoregulatory
• Gas exchange in birds

  • Birds have in their lungs large air spaces called air sacs
  • The rib cage spreads apart when a bird inhales, and a partial vacuum is created in the lungs
  • Air flows into the lungs and then into the air sacs, where much of the exchange of gas takes place
• Osmoregulation in plants

  1. Use stomata on the lower side of their leaves to control water loss

  2. Absorb more water from the soil to compensate for water depletion by transpiration

  3. Retain water in the vacuoles and have dense, fleshy cuticles to avoid lack of water
• Osmoregulation in freshwater fish

  1. Consume a regulated volume of water through the mouth and membranes of the gill

  2. Create huge volumes of urine in which a lot of salt is lost

  3. Supplement salt through mitochondrial-rich cells in the gills
• Gas exchange in mammals

  • A rich network of blood vessels for transporting gases surrounds each alveolus
  • Mammals have a dome-shaped diaphragm that separates the thorax from the abdomen, providing a separate the chest cavity for breathing and blood circulating
  • The diaphragm contracts and flattens to create a partial vacuum in the lungs during inhalation