Bio Notes PDF

Bio Notes Tropism Tropism refers to the directional growth or movement of an organism or its parts in response to environmental stimuli. It is commonly observed in plants, where growth occurs towards or away from stimuli such as light (phototropism), gravity (gravitropism), or water (hydrotropism)....

Bio Notes Tropism Tropism refers to the directional growth or movement of an organism or its parts in response to environmental stimuli. It is commonly observed in plants, where growth occurs towards or away from stimuli such as light (phototropism), gravity (gravitropism), or water (hydrotropism). In a broader biological context, tropism can also describe the behavior of viruses and pathogens in targeting specific host tissues. Structure of the Eye The human eye is a complex sensory organ responsible for vision. Its main structures include: Cornea: A transparent layer that refracts light entering the eye. Iris: The colored part of the eye that controls the size of the pupil and regulates light entry. Pupil: The opening in the iris that allows light to enter. Lens: A flexible structure that adjusts its shape to focus light on the retina. Retina: The inner layer containing photoreceptor cells (rods and cones) that convert light into electrical impulses for visual processing. Optic Nerve: Transmits visual information from the retina to the brain. Function of Auxin Auxin is a plant hormone that plays a critical role in growth regulation. It influences various processes, including: Cell elongation: Promotes growth by loosening cell walls. Apical dominance: Suppresses lateral bud growth, ensuring that plants grow taller rather than bushier. Tropisms: Mediates responses to light and gravity by redistributing itself within plant tissues, leading to differential growth rates. Feedback Mechanism A feedback mechanism is a biological process where the output of a system influences its own activity. There are two main types: Positive Feedback: Enhances or amplifies changes (e.g., childbirth). Negative Feedback: Reduces or dampens changes, maintaining homeostasis (e.g., regulation of body temperature). Negative Feedback Loop A negative feedback loop is a control mechanism that counteracts changes in a system. For example, when body temperature rises, mechanisms are activated to cool the body down (e.g., sweating). This loop helps maintain stable internal conditions despite external fluctuations. Inheritance of Genes Inheritance refers to the genetic transmission of traits from parents to offspring. Genes, which are segments of DNA, determine specific characteristics. The principles of inheritance were first described by Gregor Mendel through his studies on pea plants, establishing foundational concepts such as dominant and recessive traits. Offspring Offspring are the descendants produced by reproduction. In sexual reproduction, offspring inherit genetic material from both parents, leading to genetic variation. In asexual reproduction, offspring are genetically identical to the parent organism. Punnett Square A Punnett square is a graphical tool used to predict the genotypic and phenotypic outcomes of genetic crosses. It illustrates how alleles from each parent combine during fertilization, helping to visualize inheritance patterns for traits governed by single genes. Natural Selection Natural selection is a fundamental mechanism of evolution proposed by Charles Darwin. It describes how individuals with advantageous traits are more likely to survive and reproduce, passing those traits on to future generations. Over time, this process can lead to adaptations within populations. Reproduction in Plants and Animals Reproduction can be classified into two main types: Asexual Reproduction: Involves a single parent organism producing genetically identical offspring (e.g., budding in yeast). Sexual Reproduction: Involves two parents contributing genetic material to produce genetically diverse offspring through processes like fertilization. In plants, reproduction can occur through flowers (sexual) or vegetative methods (asexual). In animals, sexual reproduction typically involves mating and fertilization processes.