(a) What does a root do in response to gravity? What is this phenomenon known as?
(b) What does a stem (or shoot) do in response to light? What is this phenomenon known as?
(a) What does a root do in response to gravity? What is this phenomenon known as?
(b) What does a stem (or shoot) do in response to light? What is this phenomenon known as?
(a) Gravitropism (also known as geotropism) is a turning or growth movement by a plant or fungus in response to gravity. It is a general feature of all higher and many lower plants as well as other organisms. Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull (i.e. downward) and stems grow in the opposite direction (i.e. upwards). This behaviour can be easily demonstrated with any potted plant. When laid onto its side, the growing parts of the stem begin to display negative gravitropism, growing upwards. Herbaceous (non-woody) stems are capable of a small degree of actual bending, but most of the redirected movement occurs as a consequence of root or stem growth outside.
(b) An auxin is a plant growth hormone that helps regulate shoot growth. But when sunlight varies, auxin is broken down on the sunnier side of the stem. The higher concentration of auxin on the shady side causes the plant cells on that side to grow more so it bends toward the light.
(a) Gravitropism (also known as geotropism) is a turning or growth movement by a plant or fungus in response to gravity. It is a general feature of all higher and many lower plants as well as other organisms. Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull (i.e. downward) and stems grow in the opposite direction (i.e. upwards). This behaviour can be easily demonstrated with any potted plant. When laid onto its side, the growing parts of the stem begin to display negative gravitropism, growing upwards. Herbaceous (non-woody) stems are capable of a small degree of actual bending, but most of the redirected movement occurs as a consequence of root or stem growth outside.
(b) An auxin is a plant growth hormone that helps regulate shoot growth. But when sunlight varies, auxin is broken down on the sunnier side of the stem. The higher concentration of auxin on the shady side causes the plant cells on that side to grow more so it bends toward the light.
