Unit 11: Interdependence and Biological Systems

DNA and the Fundamentals of Variation

Deoxyribonucleic Acid, commonly referred to as DNA, serves as the primary storage of genetic information within the nucleus of a cell. Genes themselves are composed of DNA. Within the study of living things, variation describes the differences between organisms. This can be categorized into two distinct types: Discontinuous Variation and Continuous Variation. Discontinuous Variation occurs when a characteristic falls into a specific group or category, with no intermediates; examples of this include blood groups and eye color. In contrast, Continuous Variation represents a complete range of measurements from one extreme to another, such as height and weight.

Classification and Vertebrates

Classification is defined as the process of grouping or categorizing living things. Scientists recognize five primary kingdoms of organisms: Animals, Fungi, Bacteria, Protists, and Plants. A major distinction in the animal kingdom is the presence of vertebrae, or a backbone. Organisms possessing a backbone are classified as vertebrates. Significant groups under this classification include Mammals, Birds, Reptiles, Amphibians, and Fish. In scientific study, a specimen refers to a dead or once-living thing that has been preserved.

Species and Human Reproduction

A species is defined as a group of similar organisms that can successfully reproduce with one another to create offspring. The process of creating offspring begins when gametes join together. In males, the sex cells are called sperm, which are produced in the testes. The structure of a sperm cell includes a head containing a cell membrane and a nucleus with $23$ chromosomes, a middle piece, and a tail designed to facilitate movement. In females, the sex cells are known as eggs, which are produced in the ovaries. Fertilization is the fusion of the nuclei of the male cell and the female cell, resulting in a new cell called a zygote. This process takes place in the oviduce (oviduct). Ovulation occurs when the egg is released from the ovary.

Plant Structure and Reproduction

Plants possess complex structures for reproduction. The male part of the flower is the stamen, consisting of the anther and the filament. The female part, often referred to as the carpel, includes the stigma, style, and ovary. Other structures include petals and the sepal. Pollination is the process where pollen is transferred from the anther to the stigma; the pollen then travels down the style to reach the ovule. In sexual reproduction, the fertilized egg becomes a zygote. Alternatively, Asexual Reproduction involves only one parent and produces genetically identical individuals without the use of sex cells. Examples of asexual reproduction include budding in yeast or taking cuttings from roots and stems. The advantages of asexual reproduction include the ability for a population to increase quickly and the guarantee that good features from the parent will be passed on. However, the disadvantages include a lack of variation or difference, making the species less resilient to diseases or changes in the climate.

Habitats, Food Chains, and Natural Selection

A habitat is the specific place where an organism lives and obtains everything it needs for survival, including food, shelter, water, and air. Typical habitats include the jungle, desert, oceans, rainforest, and the arctic. Energy flow in these environments is tracked through a food chain. A food chain always begins with a producer, which makes its own food through the process of photosynthesis using energy from the sun. The chain ends with a consumer, which can be a prey animal, a predator, or both. Natural Selection describes the fact that organisms best adapted for their environment will survive and reproduce. Adaptation is a specific feature that helps a plant or animal survive; organisms that are not well-developed for their environment will die out and may become extinct. Food webs consist of several food chains joined together, and the different feeding levels within these structures are known as trophic levels.

Biomass, Decomposition, and Life Processes

Biomass refers to the mass of living material in an organism, which is built up using energy from the sun by plants and passed down through food chains. Microorganisms are living organisms that are only visible through a microscope; the main groups include bacteria and fungi. Decomposers are organisms that feed on dead plants and animals, breaking down biomass and enabling decay. Detritus is the term for the rotten mass of decomposing plants and animals. Scavengers, such as maggots, hyenas, and vultures, also play a role in consuming dead matter. Bio-accumulation refers to the build-up of poisons along a food chain. Cellular Respiration is the chemical process where fuel is used to provide energy for life processes. These essential life processes are summarized by the acronym MRS GREN: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition. For an entity to be considered a living human organism, they must be able to carry out these processes.