Savvas Realize Topic 3 Lesson 4

Growth and Development of Organisms

• Several factors influence how organisms grow. Some are genetic characteristics, while others are related to access to resources, the environment, or responses to stimuli. To increase their chance for survival, plants and animals adapt over time.

Plant Responses & Tropisms

• Hormones control a plant's response to stimuli (ex: Auxin speeds up the rate at which plant cells grow and controls a plant's response to light). A plant's growth response toward or away from a stimulus is called a tropism (ex: touch, gravity, light).

• Plant vines show positive thigmotropism (response to touch) as they coil around an object for support.

• A plant's response to light is called phototropism, where leaves, stems, and flowers grow toward it.

• A plant's response to gravity is called gravitropism. (roots show positive g., stems show negative g.)

Seasonal Change

• A plant's response to seasonal changes in the length of day and night is called phototropism. Some plants change based on the length of night, while others don't change at all.

• As winter approaches, many plants go into a state of dormancy, a period when an organism's growth or activity stops. This helps plants survive freezing temps and a lack of water. Cooler weather and less sunlight causes leaves to stop making chlorophyll. As a result, yellow and orange pigment becomes visible.

Environmental Conditions (Plants)

• In ideal conditions, plants will reach a maximum size that is normal for its species. However, sometimes a lack of resources can affect growth.

• Plants need sunlight, water, and nutrient-rich soil to grow properly. Disease can also affect how a plant grows.

Animal Growth

• A growing embryo is called an embryo (can develop inside or outside the mother's body).

• 1.) One way embryos develop is inside an egg that is laid outside the body. Most invertebrates, fish, reptiles, and birds lay eggs. The contents of the egg provide all the nutrients embryos need.

• The eggs of land vertebrates are called amniotic eggs, which are covered with membranes and a leathery shell.

Animal Growth (cont.)

• 2.) Some embryos develop inside an egg that is retained in the mother's body (snakes, lizards, sharks). The egg yolk provides nutrients for the embryo, and it hatches either inside or outside the body.

• 3.) In placental mammals (humans), the embryo grows and develops inside the mother's body. Essential nutrients pass to the body from the mother through a placenta.

Comparing Life Cycles

• Most vertebrates look like small versions of adults when they are young. Others go through major body changes in metamorphosis.

External & Internal Factors

• Many internal and external factors affect growth. Internal factors include genetic and hormonal characteristics. External factors include the environment (which animals have no control over).

Environmental Conditions (Animals)

• Environmental conditions include access to resources, nutrition, and space.