Grade 8 Science Reviewer: Body Systems and Heredity

Vocabulary flashcards covering the human digestive and excretory body systems, plant vascular transport, and key concepts under heredity and genetics from the Grade 8 Science reviewer.

Digestive System Main Function

Breaks down food into smaller substances that the body can absorb and use for energy, growth, and repair.

Mouth

Chews food and begins digestion.

Esophagus

Moves food from the mouth to the stomach.

Stomach

Mixes food and continues chemical digestion.

Small Intestine

Completes most digestion and absorbs most nutrients into the bloodstream.

Large Intestine

Absorbs much of the remaining water from undigested food.

Rectum

Stores feces before elimination.

Anus

Removes feces from the body.

Mechanical Digestion

The physical breakdown of food into smaller pieces.

Chewing

An example of mechanical digestion that increases the surface area of food, allowing digestive enzymes to work more effectively.

Chemical Digestion

Uses digestive enzymes and other substances to break large food molecules into smaller molecules that can be absorbed.

Villi

Tiny finger-like structures contained in the inner lining of the small intestine, which is the major site of nutrient absorption.

Digestive System Sequence

Mouth $\rightarrow$ Esophagus $\rightarrow$ Stomach $\rightarrow$ Small Intestine $\rightarrow$ Large Intestine $\rightarrow$ Rectum $\rightarrow$ Anus.

Excretory System Main Function

Removes metabolic wastes from the body and helps maintain proper water and salt balance.

Kidneys

Organs that filter blood, remove metabolic wastes, produce urine, regulate water balance, and help maintain the proper balance of salts in the body.

Ureters

Structures that carry urine from the kidneys to the urinary bladder.

Urinary Bladder

Organ that stores urine.

Urethra

Structure that carries urine out of the body.

Urinary System Sequence

Kidney $\rightarrow$ Ureter $\rightarrow$ Urinary Bladder $\rightarrow$ Urethra.

Kidney Water Balance Regulation

The kidneys regulate the amount of water in the body, producing less urine during intense exercise when water is lost through sweating to conserve water.

Urine

Fluid consisting of water, metabolic wastes, excess salts, and other substances that need to be removed from the body.

Roots

Plant parts that anchor the plant in the soil, absorb water and minerals, and help support the plant.

Stem

Plant part that supports the plant and transports water, minerals, and food to different parts of the plant.

Leaves

Plant parts that serve as the major sites of photosynthesis.

Photosynthesis

Process during which plants use water, carbon dioxide, and light energy to produce glucose (food) and oxygen.

Xylem

Vascular tissue that transports water and minerals mainly from the roots toward the leaves.

Phloem

Vascular tissue that transports sugars or food produced during photosynthesis to different parts of the plant.

Cohesion

The attraction between molecules of the same substance; in plants, it causes water molecules to stick to one another to maintain a continuous column of water inside the xylem.

Adhesion

The attraction between molecules of different substances; in plants, it allows water molecules to stick to the walls of the xylem.

Heredity

The transmission of traits or characteristics from parents to their offspring.

Trait

A specific characteristic of an organism, such as height, eye color, blood type, seed color, and certain inherited conditions.

Gene

A segment of DNA that contains information for a particular trait or biological function.

Alleles

Different forms of the same gene, such as B for black seeds and b for white seeds.

Chromosome

A structure made of DNA and proteins that contains many genes.

Chromosome, DNA, and Gene Relationship

Chromosomes contain DNA, and DNA contains genes.

Genotype

The genetic combination of alleles an organism has for a particular trait, such as BB, Bb, or bb.

Phenotype

The observable characteristic produced by the genotype and other factors.

Dominant Allele

An allele that is expressed when at least one copy is present, usually represented by a capital letter such as B.

Recessive Allele

An allele that is generally expressed only when two copies are present (such as bb) and can be present without being expressed.

Homozygous

Condition where an organism has two identical alleles for a trait, such as BB or bb (homo = same).

Heterozygous

Condition where an organism has two different alleles for a trait, such as Bb (hetero = different).

Punnett Square

A tool used to predict the possible genetic combinations, genotypes, phenotypes, and expected probabilities of offspring from a cross between two parents.

Monohybrid Cross

A cross that examines the inheritance of one particular trait.

Genotypic Ratio of Heterozygous Monohybrid Cross ($Tt \times Tt$)

$1\text{ TT} : 2\text{ Tt} : 1\text{ tt}$.

Phenotypic Ratio of Heterozygous Monohybrid Cross ($Tt \times Tt$)

$3\text{ tall} : 1\text{ short}$ (or $75\%$ tall and $25\%$ short when tallness is dominant).

Cross Between $Bb \times bb$

A cross between a heterozygous black-seeded plant and a white-seeded plant resulting in expected genotypes of $50\%$ Bb and $50\%$ bb, and phenotypes of $50\%$ black seeds and $50\%$ white seeds.

Law of Dominance

Law stating that when two different alleles are present in an organism, the dominant allele is expressed, while the recessive allele is masked in the phenotype.

Law of Segregation

Law stating that the two alleles for a trait separate during the formation of gametes, so each gamete receives only one allele for that trait.

Incomplete Dominance

Occurs when neither allele completely masks the other, resulting in an intermediate or blended phenotype in the heterozygous offspring (e.g., RR red $\times$ WW white = RW pink).

Codominance

Occurs when both alleles are expressed at the same time in a heterozygous organism (e.g., RR red hair $\times$ WW white hair = RW both red and white hairs).