Biology 2026 Knowt

for people who want to lock in.

animal cell

A type of cell found in animals that has a flexible outer layer, no cell wall, and contains structures like mitochondria and a nucleus.

plant cell

A type of cell found in plants that has a strong outer wall, chloroplasts for making food from sunlight, and a large central storage space, along with structures found in animal cells.

Cell membrane

The outer layer of a cell that protects it and controls what goes in and out, made of fats and proteins.

Cell wall

A tough outer layer that gives support and protection to plant cells, fungi, and some bacteria, mainly made of cellulose in plants.

Chloroplast

A part of plant cells that helps them make food using sunlight, turning light energy into sugar.

Cytoplasm

The thick fluid inside a cell that holds organelles and where many chemical reactions happen.

Mitochondria

Parts of the cell known as the powerhouses, they produce energy by breaking down food.

Nucleus

The part of the cell that contains DNA and controls how the cell grows and divides.

vacuole

A large space in plant cells that stores water, nutrients, and waste, helping to keep the cell firm.

Ribosome

A tiny structure in all living cells that makes proteins by reading messenger RNA.

Cell

The smallest unit of life that can perform all life processes.

Tissue

A group of similar cells that work together to do a specific job.

Organ

A part of the body made of different tissues that work together to perform a specific function.

Organ system

A group of organs that work together to carry out complex tasks for the body.

Organism

A living thing that can survive on its own, made up of multiple organ systems.

Pistil

The female part of a flower, which includes the stigma, style, and ovary.

Stigma

The part of the pistil where pollen lands and starts to grow.

Style

The thin stalk of the pistil that connects the stigma to the ovary.

Ovary

The bottom part of the pistil that holds the ovules and turns into fruit after fertilization.

Petal

The colorful part of a flower that attracts insects for pollination.

Sepal

The outer part of a flower that protects the bud before it opens.

Stamen

The male part of a flower, made up of the anther and filament.

Anther

The part of the stamen that produces pollen.

Pollen

The fine powder made by the anthers that contains male reproductive cells.

Filament

The stalk of the stamen that holds up the anther.

Asexual reproduction

Reproduction that does not require male and female sex cells.

Cellular respiration

The process used by all living cells to release energy.

Genetic information

Information that determines how an organism will develop.

Photosynthesis

The process in plants that uses sunlight energy to make food.

Pollination

The transfer of pollen to the female part of the flower.

Sexual reproduction

The method of creating new offspring from two parents.

Aorta

The largest artery in the body that carries oxygenated blood away from the heart to the rest of the body.

Left Atrium

The chamber of the heart that receives oxygenated blood from the lungs through the pulmonary veins.

Right Atrium

The chamber of the heart that receives deoxygenated blood from the body through the superior and inferior vena cavae.

Left Ventricle

The chamber of the heart that pumps oxygenated blood into the aorta for distribution to the body.

Right Ventricle

The chamber of the heart that pumps deoxygenated blood to the lungs via the pulmonary artery.

Valves

Structures in the heart that prevent backflow of blood and ensure it flows in one direction.

Septum

The wall that separates the left and right sides of the heart, preventing the mixing of oxygenated and deoxygenated blood.

Pulmonary Arteries

Blood vessels that carry deoxygenated blood from the right ventricle to the lungs.

Pulmonary Veins

Blood vessels that carry oxygenated blood from the lungs to the left atrium.

Coronary Arteries

Blood vessels that supply blood to the heart muscle itself.

Pericardium

The double-walled sac that surrounds and protects the heart.

Veins

Blood vessels that carry deoxygenated blood back to the heart, typically featuring valves to prevent backflow.

Capillaries

Microscopic blood vessels where the exchange of oxygen, carbon dioxide, nutrients, and waste occurs between blood and tissues.

Arteries

Blood vessels that carry oxygenated blood away from the heart to the body's tissues, characterized by thick, elastic walls.

Mitral Valve

A valve located between the left atrium and left ventricle that prevents backflow of blood during ventricular contraction.

Pulmonary Valve

A valve situated between the right ventricle and the pulmonary artery that regulates blood flow from the heart to the lungs.

Aortic Valve

A valve located between the left ventricle and the aorta that prevents blood from flowing back into the heart after it has been pumped out.

Tricuspid Valve

A valve located between the right atrium and right ventricle that ensures one-way blood flow from the atrium to the ventricle.

Lumen

The interior space of a tubular structure, such as a blood vessel or the intestine.

Red blood cell

A type of cell in the blood responsible for transporting oxygen from the lungs to the body's tissues and returning carbon dioxide from the tissues back to the lungs.

White blood cell

A component of the immune system that helps the body fight infections and other diseases by identifying and destroying pathogens.

Plasma

The liquid component of blood that carries cells, nutrients, hormones, and waste products throughout the body.

Platelets

Small cell fragments in the blood that play a crucial role in blood clotting and wound healing by aggregating at the site of injury.

Deoxyhemoglobin

The form of hemoglobin that is not bound to oxygen, typically found in the venous blood returning to the lungs.

Oxyhemoglobin

The form of hemoglobin that is bound to oxygen, which is formed in the lungs when oxygen is inhaled and transported to the tissues.

Systole

The phase of the cardiac cycle during which the heart muscle contracts, pumping blood out of the chambers.

Diastole

The phase of the cardiac cycle during which the heart muscle relaxes, allowing the chambers to fill with blood.

Cartilage rings

Structural supports in the trachea that maintain its open shape and prevent collapse.

Ribs

Curved bones that form the rib cage, protecting the thoracic cavity and supporting the respiratory system.

Nasal cavity

The space behind the nose that filters, warms, and humidifies the air we breathe.

Epiglottis

A flap of cartilage that covers the trachea during swallowing to prevent food from entering the airway.

Pharynx

The muscular tube that connects the nasal cavity and mouth to the larynx and esophagus, playing a role in both breathing and digestion.

Diaphragm

A dome-shaped muscle that separates the thoracic cavity from the abdominal cavity and is essential for breathing.

Intercostal muscles

Muscles located between the ribs that assist in the expansion and contraction of the thoracic cavity during breathing.

Left bronchus

The airway that branches from the trachea into the left lung, allowing air to enter the left lung.

Larynx

The voice box located in the throat that houses the vocal cords and is involved in breathing and sound production.

Trachea

The windpipe that connects the larynx to the bronchi, allowing air to pass to and from the lungs.

Alveoli

Tiny air sacs in the lungs where gas exchange occurs, allowing oxygen to enter the blood and carbon dioxide to be expelled.

Right lungs

The larger of the two lungs, consisting of three lobes, responsible for gas exchange.

Respiratory System

The biological system responsible for the exchange of gases, primarily oxygen and carbon dioxide, between the body and the environment.

Circulatory System

The system that transports blood, nutrients, gases, and waste products throughout the body via the heart and blood vessels.

Lungs

The primary organs of the respiratory system, responsible for gas exchange.

Heart

The muscular organ that pumps blood throughout the circulatory system.

Diffusion

The process by which molecules move from an area of higher concentration to an area of lower concentration, resulting in the spreading out of particles.

Biconcave

A type of shape that is curved inward on both sides, commonly used to describe red blood cells that increase their surface area for oxygen absorption.

Osmosis

The movement of water molecules through a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.